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[  ], 2024

Dear Stockholder:

You are cordially invited to attend a special meeting of the stockholders of Seres Therapeutics, Inc. (“Seres,” the “Company,” “we” or “us”) to be held on [  ], 2024 at [  ], Eastern Time. You may attend online via live webcast as described in the accompanying proxy statement. The accompanying proxy statement is dated [  ], 2024, and, together with the enclosed form of proxy, is first being mailed to Seres stockholders on or about [  ], 2024.

As previously announced, on August 5, 2024, Seres and Société des Produits Nestlé S.A. (“SPN”), a wholly-owned subsidiary of Nestlé S.A., entered into an Asset Purchase Agreement (the “Purchase Agreement”) pursuant to which Seres has agreed to sell Seres’ VOWST microbiome therapeutic business (the “VOWST Business”), including inventory and equipment, certain patents and patent applications, know-how, trade secrets, trademarks, domain names, marketing authorizations and related rights, documents, materials, business records and data and contracts that are used or held for use primarily in the development, commercialization and manufacturing of the microbiome product sold under the brand name VOWST, formerly known as SER-109 (the “Product”), as provided for in accordance with the terms of the Purchase Agreement to SPN and its designated affiliates (collectively, “Nestlé Health Science”), and Nestlé Health Science will assume certain liabilities from Seres (the “Transaction”).

As consideration for the Transaction, SPN has agreed to pay Seres: (i) a cash payment, payable upon completion of the Transaction (“Closing”), of $100 million, less approximately $17.9 million owed by Seres to an affiliate of SPN as of March 31, 2024 under the existing license agreement between Seres and the SPN affiliate, less approximately CHF2.0 million in satisfaction of fees due under an existing manufacturing agreement between Seres and Bacthera AG; (ii) cash installment payments of $50 million on January 15, 2025 and $25 million on July 1, 2025 (the “Installment Payments”), conditioned on Seres’ material compliance with obligations under the Transition Services Agreement to be entered into at Closing between Seres and SPN; (iii) prepayment of a $60 million milestone payment tied to the achievement of worldwide annual net sales of the Product of $150 million (the “First Sales Milestone”), payable in cash at Closing (the “Prepaid Milestone”), which Prepaid Milestone will accrue interest at a fixed rate of 10% per annum until the First Sales Milestone is achieved and 5% per annum thereafter until the earlier of (x) the date on which the Prepaid Milestone, plus accrued interest thereon, has been repaid in full by set-off and (y) the last day of the Milestone Period (as defined below); and (iv) future milestone payments of (x) $125 million tied to the achievement of worldwide annual net sales of the Product of $400 million and (y) $150 million tied to the achievement of worldwide annual net sales of the Product of $750 million, during the period from Closing until December 31 of the calendar year in which the tenth anniversary of Closing occurs (the “Milestone Period”) (together, the “Future Milestone Payments” and, together with the Prepaid Milestone, the “Milestone Payments”).

As they are earned, the Milestone Payments will be satisfied as follows: (1) first, by set-off against all accrued interest on the Prepaid Milestone until the amount of such accrued interest has been repaid in full, (2) second, by set-off against the outstanding balance of the Prepaid Milestone until the Prepaid Milestone has been repaid in full and (3) thereafter, in cash. The Installment Payment due on July 1, 2025 will be reduced by an amount related to certain employment obligations assumed by SPN through the period prior to the Closing date.

Further, as a condition to Closing, Seres and SPN will enter into a Securities Purchase Agreement pursuant to which SPN will agree to purchase 14,285,715 shares of Seres common stock, par value $0.001 per share (“Seres common stock”), at Closing at a purchase price per share of $1.05, for an aggregate purchase price of $15 million.

Following Closing, Seres expects to focus on advancing SER-155 and Seres’ other wholly-owned cultivated live biotherapeutic candidates for medically vulnerable patient populations with potential to address large commercial opportunities. Seres will continue to be a corporation organized under the laws of the State of Delaware and its common stock will continue to be listed on Nasdaq Global Select Market under the ticker symbol “MCRB.”

At the special meeting, or any postponement or adjournment thereof, you will be asked to consider and vote upon three matters: (1) a proposal to approve the proposed sale of the VOWST Business to SPN pursuant to the terms of the Purchase Agreement (the “Transaction Proposal”); (2) a proposal to approve, on a non-binding, advisory basis, certain compensation that will or may become payable to our named executive officers in connection with the Transaction (the “Compensation Proposal”); and (3) a proposal to adjourn the special meeting to a later date or dates, if necessary, to solicit additional proxies if there are insufficient votes to approve the Transaction Proposal at the time of the special meeting (the “Adjournment Proposal”).

After careful consideration, the board of directors of Seres (the “Seres Board”) has unanimously determined that the Purchase Agreement and the transactions contemplated thereby are advisable and in the best interests of Seres and its stockholders. The Seres Board unanimously recommends that Seres’ stockholders vote: (1) “FOR” the Transaction Proposal, (2) “FOR” the Compensation Proposal and (3) “FOR” the Adjournment Proposal.

Your vote is very important. The approval of the holders of a majority of the outstanding shares of Seres common stock entitled to vote at the special meeting is required to approve the Transaction Proposal. The affirmative vote of the holders of a majority in voting power of the votes cast affirmatively or negatively at the special meeting by the holders entitled to vote thereon is required to approve the Compensation Proposal. The affirmative vote of the holders of a majority in voting power of the votes cast affirmatively or negatively at the special meeting by the holders entitled to vote thereon is required to approve the Adjournment Proposal. A failure to vote your shares of Seres common stock or an abstention from voting will have the same effect as a vote “AGAINST” the Transaction Proposal and will have no effect on the Compensation Proposal and the Adjournment Proposal. Only Seres stockholders that owned Seres common stock as of 5:00 p.m., Eastern Time, on [  ], 2024, the record date for the special meeting, will be entitled to vote at the special meeting.

Whether or not you plan to attend the special meeting, we encourage you to submit your proxy as soon as possible to make sure that your shares are represented at the special meeting.

The accompanying proxy statement provides detailed information about the Transaction, the VOWST Business and Seres. We encourage you to read the accompanying proxy statement, as well as the annexes attached thereto and the exhibits and documents incorporated by reference therein, carefully in their entirety.

Sincerely,

 

Eric D. Shaff

President and Chief Executive Officer

Cambridge, Massachusetts

[  ], 2024

Neither the U.S. Securities and Exchange Commission nor any state securities regulatory agency has approved or disapproved of the transactions described in this document or the accompanying proxy statement, including the proposed sale of the VOWST Business, passed upon the merits or fairness of such transactions, or passed upon the adequacy or accuracy of the disclosure in the accompanying proxy statement. Any representation to the contrary is a criminal offense.

 

Dear Stockholder:

We are pleased to invite you to attend, and notice is hereby given that Seres Therapeutics, Inc., a Delaware corporation (“Seres,” the “Company,” “we” or “us”), will hold, a special meeting of its stockholders virtually via the internet at [ ], Eastern Time, on [ ], 2024 for the following purposes:

Seres will transact no other business at the special meeting, except such business as may properly be brought before the special meeting or any adjournment or postponement thereof. Please refer to the proxy statement of which this notice is a part for further information with respect to the business to be transacted at the special meeting.

The special meeting will be held in a virtual meeting format only, via live webcast, and there will not be a physical meeting location. You will be able to attend the special meeting online and to vote your shares electronically at the special meeting by visiting www.virtualshareholdermeeting.com/MCRB2024SM. A secure control number that will allow you to participate in and vote at the special meeting electronically can be found on your proxy card. Please be sure to follow instructions found on your proxy card and/or voting instruction form.

The record date for the special meeting is [ ], 2024. Only Seres stockholders of record on such date are entitled to receive notice of, and to vote at, the special meeting or any adjournments or postponements thereof. Completion of the Transaction is conditioned upon approval of the Transaction Proposal by holders of a majority of the Seres common stock entitled to vote at the special meeting.

After careful consideration, the Seres Board of Directors has unanimously determined that the Purchase Agreement and the transactions contemplated thereby are advisable and in the best interests of Seres and its stockholders. The Seres Board of Directors unanimously recommends that Seres’ stockholders vote: (1) “FOR” the Transaction Proposal, (2) “FOR” the Compensation Proposal, and (3) “FOR” the Adjournment Proposal.

Your vote is very important. Whether or not you expect to attend the special meeting virtually via the special meeting website, to ensure your representation at the special meeting, we encourage you to submit a proxy to vote your shares as promptly as possible by (1) visiting the internet site listed on the proxy card, (2) calling the toll-free number listed on the proxy card or (3) submitting your proxy card by mail by using the provided self-addressed, stamped envelope. Submitting a proxy will not prevent you from voting

virtually via the special meeting website at the special meeting. Any eligible holder present virtually at the special meeting may vote at that time, thereby revoking any previous proxy. In addition, a proxy may be revoked in writing before the special meeting in the manner described in the accompanying proxy statement. If your shares are held in the name of a bank, broker or other nominee, please follow the instructions on the voting instruction card furnished by the bank, broker or other nominee.

If you own shares in “street name” through an account with a bank, broker or other nominee, then you will need to obtain a legal proxy and further instructions from your bank, broker or other nominee. Your bank, broker or other nominee cannot vote on the Transaction Proposal, the Compensation Proposal or the Adjournment Proposal without your instructions.

We urge you to carefully read the accompanying proxy statement, including the annexes attached thereto and any documents incorporated by reference therein. If you have any questions concerning the proposals in this notice, the Purchase Agreement, the Transaction or the proxy statement, would like additional copies of the proxy statement or need help voting your shares of Seres common stock, please contact the Company’s proxy solicitor below:

MacKenzie Partners, Inc.

1407 Broadway, 27^th Floor

New York, New York 10018

Email: proxy@mackenziepartners.com

Toll-Free: 1-800-322-2885

By Order of the Board of Directors,

 

Thomas J. DesRosier

Secretary

Cambridge, Massachusetts

[ ], 2024

The following are brief answers to certain questions that you, as a stockholder of Seres, may have regarding the Purchase Agreement, the Transaction and the special meeting. Seres urges you to carefully read the remainder of this proxy statement, including the documents incorporated herein by reference, because the information in this section does not provide all the information that might be important to you with respect to the Purchase Agreement, the Transaction and the special meeting.

The Transaction Proposal is a proposal to approve the sale of the VOWST Business to SPN and, in exchange therefor, SPN will assume certain liabilities with respect to the VOWST Business and pay to Seres:

As they are earned, the Milestone Payments will be satisfied as follows: (1) first, by set-off against all accrued interest on the Prepaid Milestone until the amount of such accrued interest has been repaid in full, (2) second, by set-off against the outstanding balance of the Prepaid Milestone until the Prepaid Milestone has been repaid in full and (3) thereafter, in cash. If any amount of the Prepaid Milestone (and any accrued interest thereon) remains outstanding as of following the last day of the Milestone Period, the balance thereof (together with any interest accrued thereon) will be forgiven and the right of set-off of SPN with respect thereto shall be deemed forfeited. The Installment Payment due on July 1, 2025 will be reduced by an amount related to certain employment obligations assumed by SPN through the period prior to the Closing date.

As a condition to Closing, Seres and SPN will enter into the Securities Purchase Agreement pursuant to which SPN will agree to purchase 14,285,715 shares of Seres common stock at Closing at a purchase price per share of $1.05, for an aggregate purchase price of $15 million.

The Compensation Proposal is a proposal to approve, on a non-binding, advisory basis, certain compensation that will or may be paid or become payable to our named executive officers in connection with the Transaction. The Adjournment Proposal is a proposal to adjourn the special meeting to a later date or dates, if necessary, to solicit additional proxies if there are insufficient votes to approve the Transaction Proposal at the time of the special meeting.

Whether or not you plan to attend the special meeting, we encourage you to complete, sign, date and return the enclosed proxy or submit your proxies over the Internet or by phone to ensure that your shares of Seres common stock will be represented at the special meeting. If you attend the special meeting and vote in person, your vote by ballot will revoke any proxy previously submitted.

The Seres Board unanimously recommends that you vote “FOR” the Transaction Proposal, “FOR” the Compensation Proposal and “FOR” the Adjournment Proposal.

Seres currently expects to complete the Transaction within 90 days after signing the Purchase Agreement, although Seres cannot assure completion by any particular date, if at all. Because the Transaction is subject to a number of conditions, the exact timing of the Transaction cannot be determined as of the date of this proxy statement.

The webcast of the special meeting will start at [  ], Eastern Time on [  ], 2024. If you encounter any difficulties accessing the virtual meeting during registration or at the time of the virtual meeting, please call the technical support number that will be posted online on the special meeting login page.

and other advisory services in connection with the special meeting. Forms of proxies and proxy materials may also be distributed through brokers, custodians, and other like parties to the beneficial owners of shares of Seres common stock, in which case these parties will be reimbursed for their reasonable out-of-pocket expenses.

Proxies may also be solicited in person or by telephone, facsimile, electronic mail or other electronic medium by MacKenzie or Seres and its directors and officers.

Whether or not you plan to attend the special meeting virtually, we urge you to vote by proxy to ensure your vote is counted. You may still attend the special meeting and vote virtually, if you have already voted by proxy. Please choose only one method to cast your vote by proxy. We encourage you to vote over the internet or by telephone, both of which are convenient, cost-effective and reliable alternatives to returning a proxy card by mail.

If your shares of Seres common stock are held by your broker or bank as a nominee or agent, you will have to follow the instructions provided by your broker or bank to change or revoke your proxy.

If you have questions about how to vote or change your vote, you should contact our proxy solicitor:

MacKenzie Partners, Inc.

1407 Broadway, 27^th Floor

New York, New York 10018

Email: proxy@mackenziepartners.com

Toll-Free: 1-800-322-2885

If your shares of Seres common stock are held in street name and you do not issue instructions to your broker, bank or other nominee, your broker, bank or other nominee may vote your shares at its discretion on routine matters, but may not vote your shares on non-routine matters. The Transaction Proposal, Compensation Proposal and Adjournment Proposal are non-routine matters. Accordingly, if your shares of Seres common stock are held in “street name” and you do not issue instructions to your broker, your shares of Seres common stock will not be voted at the special meeting and will not be counted for purposes of determining whether a quorum exists.

Even if you sell or otherwise transfer your shares of Seres common stock after the Record Date, we encourage you to sign, date and return the enclosed proxy or submit your proxy over the Internet or by phone or, if your shares are held in “street name” through a broker, bank or nominee, instruct your broker, bank or nominee on how to vote your shares using the voting instruction form furnished by your broker, bank or nominee.

In addition to the other information contained in or incorporated by reference into this proxy statement, you should consider carefully the following risk factors and the matters addressed in the section of this proxy statement entitled “Cautionary Statement Regarding Forward-Looking Statements.” You should also read and consider the other information included and incorporated by reference into this proxy statement, including the information set forth under the caption “Risk Factors” in Seres’ Annual Report on Form 10-K for the year ended December 31, 2023, and Quarterly Report on Form 10-Q for the quarter ended June 30, 2024. See the section of this proxy statement entitled “Questions and Additional Information.”

The completion of the Transaction is subject to a number of conditions, including the approval of the Transaction by Seres stockholders, which make the completion and timing of the Transaction uncertain. See the section entitled “The Purchase Agreement—Conditions to Completion of the Transaction” for a more detailed discussion. The failure to satisfy all of the required conditions could delay the completion of the Transaction for a significant period of time or prevent it from occurring at all. There can be no assurance that the conditions to the completion of the Transaction will be satisfied or waived or that the Transaction will be completed.

In addition, either Seres or SPN may terminate the Purchase Agreement under certain circumstances, including if the Transaction is not completed by the outside date. In certain circumstances, upon termination of the Purchase Agreement, Seres would be required to pay $4.7 million to SPN for the reimbursement of expenses. For further discussion, see the section entitled “The Purchase Agreement—Reimbursement Expense Payable by Seres.”

If the Transaction is not completed, Seres may be adversely affected and, without realizing any of the benefits of having completed the Transaction, will be subject to a number of risks, including the following:

In addition, if the Transaction is not completed, Seres could be subject to litigation related to any failure to complete the Transaction or related to any enforcement proceeding commenced against Seres to perform its obligations under the Purchase Agreement. Any of these risks could materially and adversely impact our business, financial condition, results of operations and the trading price of shares of Seres common stock.

Similarly, delays in the completion of the Transaction could, among other things, result in additional transaction costs, loss of revenue or other negative effects associated with delay and uncertainty about completion of the Transaction and could materially and adversely impact our business, financial condition, results of operations and the trading price of shares of Seres common stock.

In connection with the Transaction, SPN will assume certain liabilities with respect to the VOWST Business and pay to Seres:

As they are earned, the Milestone Payments will be satisfied as follows: (1) first, by set-off against all accrued interest on the Prepaid Milestone until the amount of such accrued interest has been repaid in full, (2) second, by set-off against the outstanding balance of the Prepaid Milestone until the Prepaid Milestone has been repaid in full and (3) thereafter, in cash. If any amount of the Prepaid Milestone (and any accrued interest thereon) remains outstanding as of following the last day of the Milestone Period, the balance thereof (together with any interest accrued thereon) will be forgiven and the right of set-off of SPN with respect thereto shall be deemed forfeited. The Installment Payment due on July 1, 2025 will be reduced by an amount related to certain employment obligations assumed by SPN through the period prior to the Closing date.

The Installment Payments and the Milestone Payments are subject to various risks and uncertainties. Seres must be in material compliance with its obligations under the Transition Services Agreement in order to receive the Installment Payments and, if it is not or if there is a dispute as to compliance, such payments could be withheld or delayed pending resolution. The Milestone Payments will be based on the achievement of specified worldwide net sales targets for the Product. Interest on the Prepaid Milestone will accrue and will reduce any corresponding Milestone Payments based on the length of time it takes to achieve the milestones. It is not possible to determine with precision as of the date of this proxy statement the amount or timing of worldwide net sales the Product will generate in the future and, therefore, it is possible that the Milestone Payments will not be earned or will be limited by lower Product net sales than anticipated. The VOWST Net Sales Projections (as defined below) set forth in this proxy statement were based on certain assumptions about the future financial performance of the Product, and there can be no assurance that such projections will be achieved or that the Milestone Payments will become payable.

Further, during the Profit Sharing Period (as defined below), Seres will be entitled to receive 50% of all Net Profit (as defined below) and will bear 50% of all Net Loss (as defined below), as applicable (the “Profit

Sharing Payments”). Amounts payable or due under the Profit Sharing Payments are uncertain and could result in financial losses or financial gains that are less than expected.

The Purchase Agreement contains non-solicitation provisions that make it substantially more difficult for Seres to sell its assets or engage in another type of acquisition transaction with a party other than SPN. Specifically, we agreed, subject to certain exceptions with respect to unsolicited bids and the exercise of fiduciary duties by the Seres Board, not to directly or indirectly solicit an Acquisition Proposal or to enter into discussions concerning, or provide confidential information in connection with any submission, announcement, proposal or offer that would reasonably be expected to lead to an Acquisition Proposal.

These non-solicitation provisions, among others contained in the Purchase Agreement, could discourage a third party that might have an interest in acquiring all or substantially all of our assets or our common stock from considering or proposing such an acquisition, even if that party were prepared to pay consideration with a higher value than the consideration paid by SPN.

In certain circumstances, upon termination of the Purchase Agreement, Seres would be required to pay $4.7 million to SPN for the reimbursement of expenses. For further discussion, see the section entitled “The Purchase Agreement—Reimbursement Expense Payable by Seres.”

We expect to incur significant expenses related to the Transaction. These expenses include, but are not limited to, financial advisory and opinion fees and expenses, legal fees, accounting fees and expenses, certain employee expenses, filing fees, printing expenses and other related fees and expenses. Many of these expenses will be payable by us regardless of whether the Transaction is completed.

Further, if the Transaction is completed, we will enter into the Transition Services Agreement, which will provide for services to be performed by Seres in order to facilitate a smooth transition of the business associated with the Product to SPN and its affiliates. Performance of our obligations under the Transition Services Agreement will incur significant financial costs and the focus and attention of our management and employee resources may be diverted from the Remaining Business.

The announcement and pendency of the Transaction, whether or not consummated, may adversely affect the trading price of our common stock as well as our relationships with existing or potential suppliers, customers, vendors, distributors, licensors, licensees, collaboration partners and other business partners, and may have an adverse effect on the business, financial condition and results of operations of Seres. The pending Transaction may cause such counterparties to seek to change existing business relationships with Seres or the VOWST Business, to forego new relationships or to enter into alternative agreements with our competitors because business partners may perceive that such new relationships are likely to be more stable.

In addition, current and prospective employees of Seres, including of the VOWST Business, may feel uncertain about their roles within Seres or the VOWST Business prior to and following the completion of Transaction, which may have an adverse effect on the Company’s ability to attract or retain key management personnel or other key employees. If key employees depart, the business of Seres, its financial condition and its results of operations may be adversely impacted.

The focus and attention of our management and employee resources may also be diverted from operational matters during the pendency of the Transaction to focus on integration matters and the consummation of the Transaction.

One of the conditions to the completion of the Transaction is the absence of any judgment or law issued or enacted by any governmental entity of competent jurisdiction, in each case that has been entered and remains and

effect that prevents, enjoins, renders illegal or prohibits the consummation of the Transaction. Accordingly, if litigation is filed challenging the Transaction and a plaintiff is successful in obtaining an order enjoining completion of the Transaction, then such order may prevent the Transaction from being completed or from being completed within the expected time frame.

The unaudited pro forma financial information of Seres in this proxy statement is presented for illustrative purposes only and is not necessarily indicative of what Seres’ actual financial position or results of operations would have been had the Transaction been completed on the dates indicated. The unaudited pro forma financial information is subject to a number of assumptions (including, but not limited to, those related to industry performance and competition, general business, economic, market and financial conditions and additional matters specific to our business) that are inherently subjective and uncertain and are beyond the control of Seres. Therefore, our actual results and financial position after the Transaction may differ materially and adversely from the unaudited pro forma financial information that is included in this proxy statement. For further discussion, see the section entitled “Financial Information—Unaudited Pro Forma Financial Information.”

In performing its financial analysis and rendering its opinion, at Seres’ direction, Houlihan Lokey reviewed and relied on, among other things, internal financial analyses and forecasts for certain aspects of our business, which were prepared by management. This prospective financial information includes assumptions regarding future operating cash flows, expenditures, and income, among other matters. This prospective financial information was not prepared with a view to public disclosure, is subject to significant economic, competitive, regulatory, industry, market and other uncertainties and may not be achieved in full, at all, or within projected timeframes. Stockholders should not place undue reliance on the prospective financial information when deciding how to vote on the Transaction Proposal or evaluating their investment in our common stock.

Seres may not be able to realize the anticipated benefits from the Transaction, including potentially deploying the proceeds from the Transaction to advance our pipeline of wholly-owned cultivated live biotherapeutic candidates. The ability of Seres to realize the anticipated benefits of the Transaction and the success of the remaining company is subject to various risks and uncertainties, including the possibility that we may not be able to successfully use our live biotherapeutic platform to build a pipeline of product candidates and develop additional marketable drugs, and the possibility that we will not be able to obtain, or experience delays in obtaining, required regulatory approvals.

Seres may also face new challenges operating as a smaller company as a result of the completion of the Transaction, including:

The Transaction will result in Seres being a smaller, less diversified company with a more limited Remaining Business concentrated on SER-155 and Seres’ other wholly-owned cultivated live biotherapeutic candidates. As a result, we may be more susceptible to changing market conditions, including fluctuations and risks particular to preclinical and clinical-stage companies, than a more diversified company, which could adversely affect our

Remaining Business, financial condition and results of operations. In addition, the diversification of our revenues, costs and cash flows will diminish following the Transaction, such that our results of operations, cash flows, working capital and financing requirements may be subject to increased volatility and our ability to fund capital expenditures and investments or satisfy other financial commitments may be diminished.

We are obligated to use the proceeds from the completion of the Transaction to fully repay our indebtedness under the Oaktree Credit Agreement. We will have broad discretion with respect to the use of the remaining proceeds of the Transaction, including for any of the purposes described in the section of this proxy statement titled “The Transaction—Effects on Seres if the Transaction is Completed and the Nature of Seres’ Business Following the Transaction.” The results and effectiveness of the use of proceeds are uncertain, and we could spend the proceeds in ways that do not improve our Remaining Business, financial condition or results of operations. Our failure to apply these funds effectively could have an adverse effect on its business, financial condition and results of operations.

The historical and pro forma financial information, including the VOWST Business’ combined financial statements, in this proxy statement is derived from the consolidated financial statements and accounting records of our operations prior to the sale of the VOWST Business. Accordingly, the historical and pro forma financial information, including the VOWST Business’ combined financial statements, included in this proxy statement does not necessarily reflect the financial results that we would have achieved through our VOWST Business or Remaining Business during the periods presented or those that we may achieve in the future primarily as a result of significant changes to our cost structure, management, financing and business operations as a result of selling the VOWST Business and continuing operations through our Remaining Business. For additional information about our past financial performance and the basis of presentation of our historical and pro forma financial information, please refer to the section of this proxy statement titled “Financial Information”, in addition to our audited consolidated financial statements for the years ended December 31, 2023 and 2022 contained in our Current Report on Form 8-K filed on August 15, 2024, which are incorporated by reference into this proxy statement.

This proxy statement and the documents incorporated by reference in this proxy statement may contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Exchange Act that do not directly or exclusively relate to historical facts, including, without limitation, statements relating to the completion of the Transaction. Forward-looking statements may be identified by the context of the statement and generally arise when Seres or its management is discussing its beliefs, estimates or expectations. Such statements generally include words such as “believes,” “plans,” “intends,” “targets,” “aims,” “will,” “expects,” “estimates,” “suggests,” “anticipates,” “outlook,” “continues,” “could,” “should,” “would,” “may,” “seeks,” “might,” “predicts,” “projects,” or other similar expressions, or the negative of these terms or comparable terminology. Forward-looking statements are prospective in nature and are not based on historical facts, but rather on our current plans and expectations and projections of our management about future events and are therefore subject to risks and uncertainties, many of which are outside Seres’ control, and which could cause actual results to differ materially from those included in or contemplated or implied by the forward-looking statements. Such risks and uncertainties include, without limitation:

These and other risks and uncertainties are identified in more detail in Seres’ reports and filings with the SEC, including the risks and uncertainties set forth in Item 1A under the heading Risk Factors in our Annual Report on Form 10-K for the year ended December 31, 2023, filed with the SEC on March 5, 2024, our Quarterly Report on Form 10-Q for the fiscal quarter ended on June 30, 2024, filed with the SEC on August 13, 2024, and other subsequent periodic reports we file with the SEC, as well as those described in this proxy statement under “Risk Factors”.

While the list of factors presented here is considered representative, this list should not be considered to be a complete statement of all potential risks and uncertainties. Any forward-looking statements contained or incorporated by reference in this proxy statement are made only as of the date of this proxy statement, and we undertake no obligation to update forward-looking statements to reflect developments or information obtained after the date hereof and disclaim any obligation to do so other than as may be required by applicable law. Readers are cautioned not to place undue reliance on any of these forward-looking statements.

101 Cambridgepark Drive

Cambridge, Massachusetts 02140

(617) 945-9626

Seres Therapeutics, Inc. is a commercial-stage microbiome therapeutics company focused on the development and commercialization of a novel class of biological drugs, which are designed to treat disease by modulating the microbiome to restore health by repairing the function of a disrupted microbiome to a non-disease state. Seres’ first drug, VOWST™, formerly called SER-109, was approved by the FDA on April 26, 2023, to prevent recurrence of CDI in patients 18 or older following antibacterial treatment for rCDI. Seres’ drug discovery and development pipeline includes other pre-clinical and clinical-stage assets, including SER-155 in a Phase 1b study in patients receiving allogeneic hematopoietic stem cell transplantation. Results from the second cohort in this study are expected in September 2024. SER-155 has potential to reduce the incidence and severity of gastrointestinal and related bloodstream infections, and the incidence of acute graft-versus-host disease.

Seres is a corporation organized under the laws of the State of Delaware. Shares of Seres common stock are listed on the Nasdaq under the symbol “MCRB.”

Our principal executive offices are located at 101 Cambridgepark Drive, Cambridge, Massachusetts 02140.

SPN is a société anonyme organized under the laws of Switzerland and a wholly-owned subsidiary of Swiss-based, Food, Health and Wellness company, Nestlé S.A. Nestlé Health Science is a global division of Nestlé and a leader in the science of nutrition committed to redefining the management of health, offering an extensive portfolio of science-based consumer health, medical nutrition, pharmaceutical therapies, and vitamin and supplement brands.

This proxy statement is being provided to the stockholders of Seres as part of a solicitation of proxies by the Seres Board for use at the special meeting to be held at the time and place specified below, and at any properly convened meeting following an adjournment or postponement thereof. This proxy statement, including the information incorporated herein by reference and the annexes attached hereto, provides stockholders of Seres with the information they need to know to be able to vote or instruct their vote to be cast at the special meeting.

The Seres special meeting is scheduled to be held on [ ], 2024, at [ ], Eastern Time. You may attend online via live webcast by visiting www.virtualshareholdermeeting.com/MCRB2024SM and providing the control number on your proxy card. Please be sure to follow instructions found on your proxy card and/or voting instruction form. The special meeting will be held solely by means of remote communication rather than in person.

The webcast of the special meeting will start at [ ], Eastern Time, on [ ], 2024 at www.virtualshareholdermeeting.com/MCRB2024SM. A secure control number that will allow you to participate in and vote at the special meeting electronically can be found on the enclosed proxy card.

The online meeting platform is fully supported across browsers (Internet Explorer, Firefox, Chrome, and Safari) and devices (desktops, laptops, tablets, and cell phones) running the most updated version of applicable software and plugins. Participants should ensure that they have a strong Wi-Fi connection if they intend to participate in the special meeting online. Participants should also give themselves plenty of time to log in and ensure that they can hear streaming audio prior to the start of the special meeting.

If you encounter any difficulties accessing the virtual meeting during registration or at the time of the virtual meeting, please call the technical support number that will be posted online on the special meeting login page.

At the special meeting, Seres stockholders will be asked to consider and vote on the Transaction Proposal, the Compensation Proposal and the Adjournment Proposal.

Completion of the Transaction under the terms of the Purchase Agreement is conditioned on approval of the holders of a majority of the outstanding shares of Seres common stock entitled to vote at the special meeting. The Compensation Proposal and the Adjournment Proposal each require the affirmative vote of the holders of a majority of the shares of Seres common stock voting on the proposal at the special meeting.

After careful consideration, the Seres Board has unanimously (i) determined that the Purchase Agreement and the transactions contemplated thereby are advisable and in the best interests of Seres and its stockholders; (ii) approved the execution, delivery and performance by Seres of the Purchase Agreement and the consummation of the transactions contemplated thereby; (iii) directed that a proposal to approve the Transaction be submitted to the stockholders of Seres for approval at the special meeting; and (iv) recommended that Seres’ stockholders approve the Transaction.

Certain factors considered by the Seres Board in making such unanimous determination and approval are described in the section entitled “The Transaction—Recommendation of the Seres Board and Reasons for the Transaction.” The Seres Board unanimously recommends that stockholders vote: (1) “FOR” the Transaction Proposal; (2) “FOR” the Compensation Proposal; and (3) “FOR” the Adjournment Proposal.

Only holders of record of Seres common stock at 5:00 p.m., Eastern Time, on [ ], 2024, the Record Date for the special meeting, will be entitled to notice of, and to vote at, the special meeting or any adjournments or postponements of the special meeting. At 5:00 p.m., Eastern Time, on the Record Date, [ ] shares of Seres common stock were issued and outstanding.

Holders of record of Seres common stock are entitled to one vote for each share of Seres common stock they own at 5:00 p.m., Eastern Time, on the Record Date.

The presence at the special meeting, virtually or by proxy, of the holders of a majority in voting power of the capital stock of Seres issued and outstanding and entitled to vote on the Record Date will constitute a quorum. Any shares of Seres common stock held by Seres or by any of its subsidiaries are not considered to be outstanding for purposes of determining a quorum. There must be a quorum for business to be conducted at the special meeting. Failure of a quorum to be represented at the special meeting may result in an adjournment of the special meeting and may subject us to additional expense. If you submit a properly executed proxy card, even if you abstain from voting, your shares will be counted for purposes of calculating whether a quorum is present at the special meeting.

The Transaction Proposal requires the affirmative vote of the holders of a majority of the outstanding shares of Seres common stock entitled to vote at the special meeting. The Compensation Proposal requires the affirmative vote of the holders of a majority of the shares of Seres common stock voting on the Compensation Proposal at the special meeting. The Adjournment Proposal requires the affirmative vote of the holders of a majority of the shares of Seres common stock voting on the Adjournment Proposal at the special meeting. An abstention will have the same effect as a vote “AGAINST” the Transaction Proposal and will have no effect on the Compensation Proposal and the Adjournment Proposal.

Concurrently with the execution of the Purchase Agreement, Seres’ directors and executive officers and certain stockholders affiliated with Flagship Pioneering, Inc. entered into support agreements with Seres and SPN (the “Support Agreements”), pursuant to which, among other things and subject to the terms and conditions therein, such parties agreed, solely in their capacities as holders of shares of Common Stock (collectively, the “Subject Shares”), to vote all Subject Shares beneficially owned by such parties at every meeting of the stockholders of Seres (including the special meeting to consider the transactions contemplated by the Purchase Agreement) (i) in favor of adopting and approving the Purchase Agreement and the transactions contemplated by the Purchase Agreement, (ii) against any proposal that would otherwise be reasonably be expected to adversely affect the transactions contemplated by the Purchase Agreement, (iii) against any Acquisition Proposal, and (iv) in favor of approving any proposal to adjourn or postpone the special meeting of stockholders to a later date, if there are not sufficient votes for the adoption of the Purchase Agreement on the date on which such meeting is held. In addition, each stockholder party to a Support Agreement provided an irrevocable proxy to SPN to vote such party’s Subject Shares in favor of adopting and approving the Purchase Agreement and the transactions contemplated by the Purchase Agreement.

As of 5:00 p.m., Eastern Time, on the Record Date, the directors and executive officers of Seres were entitled to vote [ ] shares of Seres common stock, or approximately [ ]% of the shares Seres common stock issued and outstanding on that date and entitled to vote at the special meeting.

An abstention occurs when a stockholder attends a meeting, virtually or by proxy, but abstains from voting. At the special meeting, abstentions will be counted in determining whether a quorum is present. Abstentions and a failure to vote your shares of Seres common stock (including the failure of a record owner to execute and return a proxy card and the failure of a beneficial owner of shares held in “street name” by a broker to give voting instructions to the broker) will have the same effect as a vote “AGAINST” the Transaction Proposal and will have no effect on the Compensation Proposal and the Adjournment Proposal.

If no instruction as to how to vote is given (including an instruction to abstain) in an executed, duly returned and not revoked proxy, the proxy will be voted “FOR” the Transaction Proposal, “FOR” the Compensation Proposal and “FOR” the Adjournment Proposal.

Brokers, bankers and other nominees who hold shares on behalf of their customers may not give a proxy to Seres to vote those shares with respect to the Transaction Proposal, the Compensation Proposal and the Adjournment Proposal without specific instructions from their customers, as banks, brokers and other nominees do not have discretionary voting power on “non-routine” matters like the Transaction Proposal, the Compensation Proposal and the Adjournment Proposal. When a bank, broker or other nominee refrains from voting your shares on a particular proposal because the bank, broker or other nominee has not received your instructions and has discretionary authority to vote on the “routine” matters to be considered, it is called a “broker non-vote.” Because there are no routine matters to be considered at the special meeting, there should be no broker non-votes.

If you are a registered stockholder and you do not sign and return your proxy card or vote by telephone, over the internet or virtually, your shares will not be voted at the special meeting and will not be counted for purposes of determining whether a quorum exists. A failure to vote your shares of Seres common stock (including the failure of a record owner to execute and return a proxy card and the failure of a beneficial owner of shares held in “street name” by a broker to give voting instructions to the broker) will have the same effect as a vote “AGAINST” the Transaction Proposal and will have no effect on the Compensation Proposal and the Adjournment Proposal.

If your shares are held in “street name” and you do not issue instructions to your broker, your broker may vote your shares at its discretion on routine matters, but may not vote your shares on non-routine matters. All of the proposals in this proxy statement are non-routine matters. Accordingly, if your shares are held in street name and you do not issue instructions to your broker, your shares will not be voted at the special meeting and will not be counted for purposes of determining whether a quorum exists, which will have the same effect as a vote “AGAINST” the Transaction Proposal and will have no effect on the Compensation Proposal and the Adjournment Proposal. For shares of Seres common stock held in “street name,” only shares of common stock affirmatively voted “FOR” the Transaction Proposal and “FOR” the Adjournment Proposal will be counted as a vote in favor of such proposal.

You may authorize the persons named as proxies on the proxy card to vote your shares by returning the proxy card by mail, through the internet, or by telephone. Although Seres offers multiple different voting methods, Seres encourages you to vote over the internet or by phone as Seres believes they are the most cost-effective methods. We also recommend that you vote as soon as possible, even if you are planning to attend the special meeting virtually, so that the vote count will not be delayed. If you choose to vote your shares over the internet or by telephone, there is no need for you to mail back your proxy card.

If you plan to attend the special meeting and wish to vote virtually, you must access the meeting website at www.virtualshareholdermeeting.com/MCRB2024SM and provide the control number on your proxy card. Please be sure to follow instructions found on your proxy card and/or voting instruction form.

To vote over the internet, follow the instructions printed on your proxy card. If you vote over the internet, you do not have to mail in a proxy card.

To vote by telephone, follow the instructions printed on your proxy card. If you vote by telephone, you do not have to mail in a proxy card.

To vote by proxy card, complete and sign the proxy card and mail it to the address indicated on the proxy card.

If you sign and return your signed proxy card without indicating how you want your shares of Seres common stock to be voted, your shares of Seres common stock will be voted “FOR” the Transaction Proposal, “FOR” the Compensation Proposal and “FOR” the Adjournment Proposal. Proxy cards that are returned without a signature will not be counted as present at the special meeting and cannot be voted.

If your shares are held by your broker, bank or other nominee, you will receive a form from your broker, bank or other nominee seeking instruction as to how your shares should be voted. You should contact your broker, bank or other nominee with questions about how to provide or revoke your instructions.

If you are a Seres stockholder of record, you may revoke your proxy and change your vote by following one of the below procedures:

If your shares are held in “street name,” you may submit new voting instructions with a later date by contacting your bank, brokerage firm, or other nominee. After following instructions found on your proxy card and/or voting instruction form, you may also vote online during the special meeting, which will have the effect of revoking any previously submitted voting instructions.

The Seres Board is soliciting your proxy, and Seres will bear the cost of soliciting proxies. MacKenzie has been retained to assist with the solicitation of proxies. MacKenzie will be paid a solicitation fee of $15,000 and will be reimbursed for its reasonable out-of-pocket expenses for these and other advisory services in connection with the special meeting. Forms of proxies and proxy materials may also be distributed through brokers, custodians, and other like parties to the beneficial owners of shares of Seres common stock, in which case these parties will be reimbursed for their reasonable out-of-pocket expenses. Proxies may also be solicited in person or by telephone, facsimile, electronic mail or other electronic medium by MacKenzie or Seres and its directors and officers.

If you encounter any difficulties accessing the meeting online during the check-in or meeting time, please call the technical support number that will be posted online on the special meeting login page.

Representatives of Broadridge will tabulate the votes and act as inspector of election.

Seres is not required to notify any stockholder of any adjournment of less than 30 days if the time and place of the adjourned meeting, and the means of remote communication, if any, by which stockholders and proxyholders may be deemed to be present in person and vote at such adjourned meeting, are announced at the meeting at which adjournment is taken, unless after the adjournment a new record date is fixed for the adjourned meeting. At the adjourned meeting, Seres may transact any business that might have been transacted at the original special meeting.

The SEC’s rules permit us and banks, brokers, or other agents to deliver a single set of proxy materials to one address shared by two or more of our stockholders. This delivery method is referred to as “householding” and can result in significant cost savings. To take advantage of this opportunity, we and certain banks, brokers, or

other agents have delivered only one set of proxy materials to multiple stockholders who share an address, unless we received contrary instructions from the impacted stockholders prior to the mailing date. We agree to deliver promptly, upon written or oral request, a separate copy of the proxy materials, as requested, to any stockholder at the shared address to which a single copy of those documents was delivered. If you prefer to receive separate copies of the proxy materials, contact Broadridge Financial Solutions, Inc. at 1-866-540-7095 or in writing at Broadridge, Householding Department, 51 Mercedes Way, Edgewood, New York 11717.

If you are currently a stockholder sharing an address with another stockholder and wish to receive only one copy of future proxy materials for your household, please contact Broadridge at the above phone number or address.

If you have any questions about the special meeting, require assistance with submitting your proxy or otherwise voting your shares of our common stock, or would like copies of any of the documents referred to in this proxy statement, please contact Seres’ proxy solicitor at:

MacKenzie Partners, Inc.

1407 Broadway, 27^th Floor

New York, New York 10018

Email: proxy@mackenziepartners.com

Toll-Free: 1-800-322-2885

The following is a discussion of the Transaction. The description of the Purchase Agreement in this section and elsewhere in this proxy statement is qualified in its entirety by reference to the complete text of the Purchase Agreement, which is attached as Annex A to this proxy statement. This summary does not purport to be complete and may not contain all of the information about the Transaction that is important to you. You are encouraged to read the Purchase Agreement carefully and in its entirety, as it is the legal documents that governs the Transaction.

On August 5, 2024, we entered into the Purchase Agreement, pursuant to which we agreed, subject to the satisfaction or waiver of the conditions set forth therein, to sell our VOWST Business, including inventory and equipment, certain patents and patent applications, know-how, trade secrets, trademarks, domain names, marketing authorizations and related rights, documents, materials, business records and data and contracts that are used or held for use primarily in the development, commercialization and manufacturing of the microbiome product sold under the brand name VOWST, formerly known as SER-109 (the “Product”), as provided for in accordance with the terms of the Purchase Agreement to Nestlé Health Science, and Nestlé Health Science will assume certain liabilities from Seres (the “Transaction”).

In addition to the tangible and intangible assets sold, Seres will also transfer to Nestlé Health Science (i) the license agreement with Memorial Sloan Kettering Cancer Center (the “MSK Agreement”), (ii) the supply agreement with Genlbet, and (iii) the contract manufacturing agreement with Bacthera AG (the “Bacthera Agreement”). Seres also agreed to assign certain lease agreements at donor collection facilities located in Tempe, Arizona and Irvine, California, as well as Seres’ donor screening laboratory in Pennsylvania and Seres’ lease of laboratory and office space used for quality release testing located in Waltham, Massachusetts (the “Waltham Lease”), to SPN.

As consideration for the Transaction, SPN has agreed to pay to Seres the Transaction Consideration consisting of the following:

As they are earned, the Milestone Payments will be satisfied as follows: (1) first, by set-off against all accrued interest on the Prepaid Milestone until the amount of such accrued interest has been repaid in full, (2) second, by set-off against the outstanding balance of the Prepaid Milestone until the Prepaid Milestone has been repaid in full and (3) thereafter, in cash. If any amount of the Prepaid Milestone (and any accrued interest thereon) remains outstanding as of following the last day of the Milestone Period, the balance thereof (together with any interest accrued thereon) will be forgiven and the right of set-off of SPN with respect thereto shall be deemed forfeited by SPN. The Installment Payment due on July 1, 2025 will be reduced by an amount related to certain employment obligations assumed by SPN through the period prior to the Closing date.

At Closing, in exchange for a payment to be made by SPN to Bacthera AG, the Bacthera Agreement will be terminated and each of Bacthera AG and Seres will release one another from any losses, liabilities or other obligations arising thereunder with respect to the period ending as of the date of the Closing, including without limitation any milestone payments required to be paid to Bacthera AG thereunder.

Pursuant to the Purchase Agreement, Seres and Nestlé Health Science will share 50/50 in the net profit or net loss achieved during the Profit Sharing Period from the date of Closing until December 31, 2025, with the net profit or net loss calculated as (i) the net sales of VOWST in the United States and Canada, plus (ii) other income received from a third party that is attributable to VOWST in the United States or Canada in connection with the grant of a license or sublicense with respect to VOWST in the United States and Canada as described in the Purchase Agreement, minus (iii) allowable expenses directly attributable or reasonably allocable to certain development activities, commercialization activities, medical affairs activities, manufacturing activities or other relevant activities, as described in the Purchase Agreement. During the Profit Sharing Period, Seres will reimburse Nestlé Health Science for (i) certain payments under the MSK Agreement, (ii) certain costs incurred in connection with an ongoing post-marketing safety study of the Product and (iii) the Lease Expenses, consisting of 80.1% of all rent and other costs due to the landlord under the lease for Seres’ Waltham facility.

The Seres Board and management team regularly evaluate the Company’s performance, risks, strategy and competitive position, as well as potential opportunities for business combinations, acquisitions, divestitures and other financial and strategic alternatives to enhance shareholder value. The Seres Board has also advised management to consult with and obtain guidance from certain members of the Seres Board, namely Stephen Berenson, Kurt Graves, Paul Biondi and Richard Kender (collectively, the “Transaction Committee”), on strategic transactions due to these members’ extensive experience with strategic transactions and company reorganizations.

On January 9, 2016, Seres entered into a Collaboration and License Agreement with Nestec, Ltd., which was succeeded by SPN, for the development and commercialization throughout the world, other than the United States and Canada, of certain of its product candidates in development, including those for the treatment of Clostridioides difficile infection (“CDI”) and the prevention of recurrent CDI (“rCDI”). On July 1, 2021, Seres entered into a License Agreement with an affiliate of SPN, pursuant to which Seres granted to such affiliate a license to commercialize in the United States and Canada products developed by Seres for the treatment of CDI and the prevention of rCDI (the “2021 License Agreement”). On November 8, 2021, Seres entered into a Long Term Manufacturing Agreement with Bacthera to build a dedicated production suite for the purpose of manufacturing the commercial supply of VOWST (as amended, the “Bacthera Agreement”), pursuant to which Seres agreed to make payments upon achievement of certain construction milestones by Bacthera.

On April 26, 2023, VOWST was approved by the U.S. Food and Drug Administration (the “FDA”) to prevent the recurrence of CDI in patients 18 years or older following antibacterial treatment of rCDI and in June 2023, Seres and Nestlé Health Science commercially launched VOWST in the United States.

On April 27, 2023, Seres entered into a Credit Agreement and Guaranty (the “Credit Agreement”) with, among others, Oaktree Fund Administration, LLC, in its capacity as administrative agent (“Oaktree”). The Credit Agreement established a term loan facility of $250 million, of which the first tranche of $110 million was funded to Seres on the closing date of the Credit Agreement. The second tranche of $45 million becomes available to the Company upon the achievement of trailing 6-month VOWST net sales of at least $35 million, no later than September 30, 2024, among other conditions (“Tranche B”).

After the FDA approval of VOWST, the Transaction Committee met regularly with Seres management to discuss strategic options for the Company given the Company’s limited cash resources, the timing of development of SER-155, the Company’s next product candidate following VOWST, the time needed to ramp up sales of VOWST, and the Company’s concerns about Nestlé Health Science’s commitment to commercializing VOWST due to Nestlé Health Science’s indication that it was disappointed with Seres’ efforts to pursue regulatory approval for VOWST outside of the United States and Canada and Nestlé Health Science’s concerns related to the increased costs to produce VOWST.

In May 2023, Seres management, with the assistance of representatives of Lazard, Inc. (“Lazard”), contacted six pharmaceutical companies to determine their interest in an acquisition of VOWST. Of these companies, four declined and two (“Party A” and “Party B”) expressed interest.

In June 2023, Party A and Party B entered into confidentiality agreements with Seres and were provided access to the Company’s virtual data room. Party A and Party B then conducted diligence on the Company and met multiple times with members of Seres management in due diligence sessions.

On September 13, 2023, the Seres Board, with members of Seres management and representatives from Lazard present, held a meeting to discuss strategic options for VOWST and the Company. At the meeting, the Seres Board considered continuing its collaboration with Nestlé Health Science for the commercialization of VOWST, finding a new collaborator for the commercialization of VOWST, selling Seres’ interest in VOWST or acquiring Nestlé Health Science’s interest in VOWST, and a potential merger or sale of the Company. On the basis of these discussions, the Seres Board advised management to pursue a reduction in force while continuing to advance each of the above options.

In September 2023, Party B informed Seres that they would not be proceeding with an acquisition of VOWST, and in October 2023, Party A did the same.

On October 12, 2023, Eric Shaff, Seres’ Chief Executive Officer, and Thomas DesRosier, Seres’ Chief Legal Officer, met with the Transaction Committee to discuss two potential options for selling Seres’ interest in VOWST to Nestlé Health Science, which included an immediate sale of Seres’ interest and a staged sale of Seres’ interest with Nestlé Health Science assuming responsibility for manufacturing activities by 2027. Based on these discussions, the Transaction Committee advised management to pursue negotiations with Nestlé Health Science and to propose the staged sale of Seres’ interest in VOWST.

On October 13, 2023, Mr. DesRosier sent an email to Martin Hendrix, Nestlé Health Science’s Head of Global Business Development and M&A, outlining terms for discussion of a potential purchase by Nestlé Health Science of Seres’ interest in VOWST, which included an upfront payment of $400 million, up to $200 million in sales milestones, royalty payments beginning in 2027, and supplying VOWST to Nestlé Health Science at a fixed cost per patient pack, rather than continuing to share the actual cost of manufacturing, until completing the transfer of manufacturing responsibilities by 2027.

On October 26, 2023, Messrs. Shaff, DesRosier and Hendrix had a phone call during which Mr. Hendrix indicated that, while he was not empowered at that time to negotiate a transaction for the acquisition of VOWST, he believed that Nestlé Health Science might be interested in pursuing discussions and more amenable to a potential transaction on the following terms: an upfront payment of $100 million, up to $75 million to provide for the capital expenditure obligations under the Bacthera Agreement, an option to acquire Seres’ share of VOWST in three years for $150 million, continuing with the same sales milestones under the 2021 License Agreement and royalties at a rates lower than under the 2021 License Agreement, and Seres providing VOWST to Nestlé Health Science at a fixed cost per patient pack, rather than continuing to share the actual cost of manufacturing (collectively, the “October 26 Indicative Terms”).

On October 29, 2023, the Seres Board, with members of Seres management present, held a meeting to discuss a reduction-in-force and strategic restructuring to prioritize the commercialization of VOWST and the completion of the Phase 1b study of SER-155 (the “Restructuring”). The Seres Board approved the Restructuring and advised management to continue discussions with Nestlé Health Science and business development and financing activities to strengthen the Company’s balance sheet.

In October and November 2023, Seres explored financing opportunities, but was unable to complete a financing due, in part, to potential investors’ concern about the uncertainty of VOWST’s commercial trajectory and the lack of visibility into Nestlé Health Science’s support of VOWST.

On November 2, 2023, Seres announced its third quarter financial results, including net sales for VOWST of $7.6 million for the quarter. The Company also announced the Restructuring. As a result of the Restructuring, Seres reduced its workforce by 41% and scaled down its non-partnered research and development programs. Seres anticipated that its cash, cash equivalents and investments as of September 30, 2023 in conjunction with the anticipated savings from the Restructuring and the expected receipt of Tranche B would support its operations into the fourth quarter of 2024.

On November 28, 2023, the Transaction Committee held a meeting with members of Seres management to discuss the October 26 Indicative Terms. Based on these discussions, the Transaction Committee advised management to continue discussions with Nestlé Health Science.

On November 30, 2023, Messrs. DesRosier and Hendrix had a phone call to discuss the October 26 Indicative Terms. Mr. DesRosier proposed additional terms that would provide Seres with more cash, including an equity investment in Seres and pre-payment of inventory.

On December 7, 2023, the Seres Board held a meeting, with members of Seres management present. Mr. Shaff provided an update since the September Board meeting on the feasibility of various strategic alternatives and explained that multiple alternatives requiring counterparty interest were not actionable given Nestlé Health Science’s control of VOWST marketing and sales, the early stage of SER-155 development, and the Company’s current cash runway. Given these limitations, the Seres Board discussed restructuring the existing collaboration with Nestlé Health Science, raising additional equity capital in the first quarter of 2024, and exploring further employee cuts. Based on these discussions, the Seres Board advised management to continue pursuing discussions with Nestlé Health Science and other strategic alternatives.

From December 2023 to May 2024, Nestlé Health Science conducted diligence on the VOWST supply chain, including a site visit to the production suite being constructed by Bacthera for the commercial supply of VOWST.

On December 15, 2023, Mr. DesRosier emailed the Transaction Committee to provide them an update on discussions with Nestlé Health Science and their diligence requests.

In January and February 2024, Seres management and Lazard contacted ten biotechnology companies to determine their interest in a merger with the Company, all of which declined to proceed.

On February 24, 2024, Mr. DesRosier and Mr. Hendrix had a phone call during which they discussed Nestlé Health Science’s deliberations on various strategic options for VOWST. On February 25, 2024, Mr. DesRosier updated the Transaction Committee by email regarding the call.

On March 5, 2024, Seres announced its year-end financial results for 2023, including $10.4 million of net sales for VOWST in the fourth quarter of 2023 and $19.6 million net sales since the launch of VOWST in June 2023. The Company maintained its projected cash runway of into the fourth quarter of 2024.

On March 14, 2024, Messrs. Hendrix and DesRosier had a call during which Mr. Hendrix informed Mr. DesRosier that Nestlé Health Science would be more interested in pursuing a proposed transaction whereby Nestlé Health Science would acquire Seres’ interest in VOWST in one phase, rather than the staged acquisition that Seres and Nestlé Health Science had previously discussed, and that in the coming days he would communicate the terms under which Nestlé Health Science would propose to effect such an acquisition. On March 16, 2024, Mr. DesRosier updated the Transaction Committee by email regarding the call.

On March 18, 2024, Messrs. Shaff, DesRosier and Hendrix had a phone call during which Mr. Hendrix indicated that Nestlé Health Science was interested in pursuing a transaction with an upfront payment of $60 million to acquire Seres’ interest in VOWST, the purchase by Nestlé Health Science of up to $15 million of shares of Seres’ common stock, continuation of the 50/50 profit/loss sharing under the 2021 License Agreement, a deferred payment at the end of 2025 of $60 million in cash, increased sales milestone amounts, and beginning in 2026, only royalty payments on sales to be made to Seres (collectively, the “March 18 Indicative Terms”). During the discussion, Mr. Hendrix also stipulated that the Bacthera Agreement would remain the responsibility of Seres.

On March 24, 2024, the Transaction Committee held a meeting with members of Seres management to discuss the March 18 Indicative Terms and counter terms from Seres.

On March 27, 2024, Mr. Shaff sent revised terms by email to Mr. Hendrix, which were discussed during a phone call that same day between Messrs. Shaff, DesRosier and Hendrix. The revised terms included an upfront payment of $150 million to acquire Seres’ interest in VOWST, comprised of $60 million in cash and, in lieu of royalties, the net present value of such royalties, Nestlé Health Science purchasing $88 million of inventory, Nestlé Health Science reimbursing Seres for the amount of any exit fee negotiated by Seres with Bacthera to terminate the Bacthera Agreement, and capping the portion of Seres’ share of losses at $5 million per quarter.

On March 28, 2024, Messrs. Shaff, DesRosier and Hendrix and Claudio Kuoni, General Counsel for Nestlé Health Science, had a phone call during which they discussed Oaktree’s significant concern about Seres’ financial position and the need to obtain Oaktree’s consent for a potential sale of Seres’ interest in VOWST, capital expenditure obligations under the Bacthera Agreement and splitting the cost of an exit price if the agreement were terminated, and valuation calculations. Mr. Hendrix rejected the size of the upfront payment, noting that it put too much of the commercial risk for VOWST on Nestlé Health Science. Following the call, Mr. Shaff provided an update by email to the members of the Transaction Committee.

Also on March 28, 2024, Mr. Shaff sent revised terms by email to Mr. Hendrix, which included an upfront payment of $130 million, Nestlé Health Science reimbursing Seres for 50% of any exit price negotiated with Bacthera to terminate the Bacthera Agreement, capping Seres’ share of losses at $8 million per quarter, a net payment of $52 million to Seres to settle working capital balances between the companies, and in lieu of all royalties after 2025, two deferred payments of $75 million in 2025 equal to the present value of the royalties. Mr. Shaff also sent the revised terms and a letter by email to Anna Mohl, Chief Executive Officer of Nestlé Health Science, in which he explained that, due to Seres’ limited cash resources, Oaktree was very concerned about the Company’s financial position, employee retention was becoming a challenge, and there could be an impact to the integrity of the VOWST supply chain if a transaction was not consummated. Mr. Shaff also noted that the Company’s financial advisors did not think Seres could raise additional funds from an equity financing without showing positive VOWST commercial results, which were not anticipated for the first quarter of 2024. Mr. Shaff then summarized the key points of Seres’ revised terms.

On April 1, 2024, Mr. Shaff sent an email to the Seres Board updating the Seres Board on negotiations with Nestlé Health Science.

On April 17, 2024, representatives of Evercore Group LLC (“Evercore”), the investment bank engaged by Nestlé Health Science in connection with a potential transaction with Seres, sent a written proposal on behalf of Nestlé Health Science to representatives of Lazard, proposing the acquisition of Seres’ interest in VOWST by Nestlé Health Science on the following terms: an upfront payment of $100 million, continued profit/loss sharing through December 31, 2025 with no cap on Seres’ share of losses, a deferred payment of $50 million in 2025, a decrease in the sales targets required to trigger the sales milestones payments under the 2021 License Agreement, no royalties, $75 million of senior secured debt to be provided by Nestlé Health Science to Seres, and Seres’ agreement to not compete against Nestlé Health Science in CDI for 5 years (collectively, the “April 17 Proposal”).

On April 19, 2024, Seres received a letter from the Listing Qualifications Department of The Nasdaq Stock Market LLC notifying the Company that, for the last 30 consecutive business days, the bid price for the Company’s common stock had closed below the $1.00 per share minimum bid price requirement for continued inclusion on The Nasdaq Global Select Market (the “Bid Price Requirement”) and that the Company had an initial compliance period of 180 calendar days from receipt of the letter, or until October 16, 2024, to regain compliance with the Bid Price Requirement.

On April 22, 2024, the Transaction Committee met with members of Seres management and representatives from Lazard and Latham & Watkins LLP (“Latham”), outside counsel to Seres, to discuss the April 17 Proposal. Mr. Shaff presented management’s primary considerations for a counter proposal. Mr. Shaff proposed that the senior secured loan be replaced by a combination of cash, equity or debt (and proposed two alternative combinations to the Transaction Committee), that Seres and Nestlé Health Science agree on a mechanism to protect the VOWST supply chain between signing and closing, including a public announcement of the transaction, limiting Nestlé Health Science’s ability to compete to CDI and Seres agreeing not to compete in CDI in perpetuity, no performance conditions on the $50 million deferred payment, and resolution on whether Nestlé Health Science would assume the Bacthera Agreement. The members of the Transaction Committee then discussed the counterproposal presented by Mr. Shaff and, on the basis of these discussions, advised management to replace the proposed secured loan with an incremental increase in the upfront payment of $25 million, a purchase by Nestlé Health Science of $25 million of Seres’ common stock, and $25 million of debt to be forgiven if the first sales milestone of $150 million (the “First Sales Milestone”) is not achieved within four years of closing of the transaction. The Transaction Committee also advised management to increase the proposed deferred payment from $50 million to $75 million. Mr. DesRosier then provided an overview of potential alternatives to the sale of VOWST, including a bankruptcy reorganization. A representative of Latham reviewed the pros and cons of such a reorganization and the members of the Transaction Committee discussed the same in detail.

On April 23, 2024, Mr. Shaff provided a summary by email to the Seres Board on the counterproposal that would be shared with Nestlé Health Science. On the same day, Messrs. Shaff, DesRosier and Hendrix, representatives of Lazard and representatives of Evercore had a call during which they discussed the counterproposal.

On April 24, 2024, representatives of Lazard on behalf of Seres provided a written counterproposal to representatives of Evercore, proposing that the $75 million senior secured debt be replaced by an incremental increase in the upfront payment of $25 million, for a total upfront payment of $125 million, a purchase by Nestlé Health Science of $25 million of Seres’ common stock, and $25 million of debt to be forgiven if the First Sales Milestone is not achieved within four years of closing of the transaction. In addition, Seres proposed a deferred payment of $75 million, limiting Nestlé Health Science’s ability to develop VOWST to CDI with Seres agreeing not to compete in CDI in perpetuity, and all outstanding working capital to be treated equally and settled through the upfront payment (collectively, the “April 24 Counterproposal”). Seres also requested that Nestlé Health Science make a determination regarding the Bacthera Agreement and that Nestlé Health Science agree to cover all related costs. Seres also requested that the parties issue a joint press release upon signing of a term sheet in order to ensure supply chain continuity.

On April 26, 2024, the Seres Board, with members of Seres management and representatives from Lazard and Latham present, held a meeting to discuss the April 17 Proposal and the April 24 Counterproposal. At the meeting, they also discussed alternatives if the transaction with Nestlé Health Science was not successful, including filing for Chapter 11 bankruptcy, and reiterated their support for the Transaction Committee to continue negotiations with Nestlé Health Science while continuing to update the Seres Board on the progress of the negotiations.

Later that day, representatives of Evercore, on behalf of Nestlé Health Science, provided a revised proposal to representatives of Lazard, proposing that the additional $25 million upfront payment, $25 million equity purchase, and $25 million of debt be replaced with a $15 million purchase of common stock by Nestlé Health Science conditioned on existing stockholders purchasing an equal amount and $60 million in senior secured debt to be provided by Nestlé Health Science, with cancellation of such debt if the First Sales Milestone is not achieved by 2028 and no cash interest payments until 2026; the deferred payment be reduced back to $50 million; no limitations on Nestlé Health Science’s ability to develop VOWST; Seres bear its share of losses for the second quarter of 2024; and the VOWST price supply proceeds for the second quarter of 2024 be netted against the amounts payable to Seres by Nestlé Health Science with Seres paying the net balance (the “April 26 Proposal”).

On April 27, 2024, the Transaction Committee met with members of Seres management and representatives from Lazard and Latham to discuss the April 26 Proposal. Mr. Shaff presented key areas of concern in the April 26 Proposal that needed to be further negotiated, specifically the proposed senior secured debt, which could prevent Seres from securing financing following the transaction, and Nestlé Health Science’s rejection of any limitations on its ability to develop VOWST, which could negatively impact Seres’ remaining pipeline following a transaction. On the basis of these discussions, the Transaction Committee advised management to submit a revised counterproposal to Nestlé Health Science based on the discussions at the meeting.

On May 1, 2024, Seres received a Notice of Default and Reservation of Rights (the “Notice”) under the Credit Agreement from Oaktree. The Notice specified that in Oaktree’s view, one or more events of default had occurred due to (i) the Company’s non-payment of a milestone payment under the Bacthera Agreement, which Oaktree characterized as “Indebtedness” that would not be permitted under the Credit Agreement and (ii) the Company’s failure to deliver written notice to Oaktree regarding such non-payment. Under the Bacthera Agreement, approximately $28 million would be due to Bacthera upon substantial completion of the production suite. However, the Company identified certain incomplete elements of the project required to satisfy the “Substantial Completion” criteria as set forth in the Bacthera Agreement. The Company commenced discussions with Bacthera to align on the steps necessary to complete those steps, which the Company determined could be completed in 2024, and the related timing of any milestone payment.

On May 4, 2024, Mr. Shaff sent a written counterproposal to Mr. Hendrix with proposed changes to the April 26 Proposal to address concerns about Seres’ financial viability and ability to secure financing following the transaction. Specifically, Seres proposed that instead of the $60 million of senior secured debt and $15 million equity investment, Nestlé Health Science would make a $75 million pre-payment of the First Sales Milestone,

which would earn interest at 5% and be either paid by offsetting the amount owed against future sales milestone payments or forgiven if the First Sales Milestone is not met by 2028 or the second sales milestone is not met by 2030; an increase of the deferred payment to $75 million; a mutual non-compete for five years; and issuance of a joint press release on the signing of a term sheet.

On May 7, 2024, Messrs. Shaff, DesRosier, and Hendrix, representatives of Lazard and representatives of Evercore had a call during which Evercore discussed the terms and rationale for a revised proposal from Nestlé Health Science.

Later that day, representatives of Evercore, on behalf of Nestlé Health Science, sent to representatives of Lazard a revised proposal and the first draft of a memorandum of understanding (“MOU”) for Nestlé Health Science to acquire Seres’ interest in VOWST for a $100 million upfront payment, the purchase by Nestlé Health Science of $15 million of Seres’ common stock, a director designation right for Nestlé Health Science, cost sharing under the same terms as the 2021 License Agreement until December 31, 2025, a deferred payment of $75 million to be paid in two tranches in 2025, a $60 million pre-payment to be fully offset by future sales milestone payments with interest accruing at 10% per year, reduced sales milestone amounts with no obligation to pay sales milestones after ten years following the closing of the transaction, no royalties, Nestlé Health Science’s assumption of the Bacthera Agreement, including upcoming milestone payments, offsetting any amounts due from Seres to Nestlé Health Science against the upfront payment, a five-year non-compete period by Seres in the area of CDI, and re-payment in full by Seres of the amounts outstanding under the Credit Agreement (the “May 7 Proposal”).

Also on May 7, 2024, the Transaction Committee met with members of Seres management and representatives from Lazard and Latham to discuss the May 7 Proposal. At the meeting, the Transaction Committee discussed recent discussions with Oaktree regarding the Notice and the Company’s position that an Event of Default (as defined in the Credit Agreement) had not occurred. On the basis of these discussions, the Transaction Committee advised management to continue discussions with Oaktree.

On May 8, 2024, the Company announced its results for the first quarter ended March 31, 2024, including net sales for VOWST of $10.1 million for the quarter. The Company continued to report that its cash and cash equivalents would be sufficient to fund its operations into the fourth quarter of 2024, assuming its ability to draw Tranche B.

On May 9, 2024, Mr. Shaff sent comments on the MOU to Mr. Hendrix and representatives of Evercore to, among other things, include certain leases among the assets to be acquired by Nestlé Health Science, increase the First Sales Milestone payment from $50 million to $60 million, reject the board designation right requested by Nestlé Health Science, include a 24-month standstill and lock-up provision on Seres common stock to be acquired by Nestlé Health Science, and revise the price for the common stock to be purchased by Nestlé Health Science to the highest of $1.00 per share, a 30% premium over the 30-day volume-weighted average price (“VWAP”), and the closing price as of immediately prior to the announcement of the acquisition.

On May 13, 2024, Mr. Hendrix sent Messrs. Shaff and DesRosier a revised MOU and communicated to Messrs. Shaff and DesRosier the importance to Nestlé Health Science of having a director on the Seres Board. The revised MOU reflected the director designation right, set the price per share for the proposed equity investment at a 10% premium to the 30-day VWAP, removed the standstill and lock-up provision, and included registration rights for the shares to be purchased by Nestlé Health Science.

Also on May 13, 2024, the Transaction Committee met with members of Seres management and representatives from Lazard and Latham to discuss the revised MOU. At the meeting, the Transaction Committee reviewed and discussed management’s proposed changes to the MOU to set the price per share at the higher of $0.80 or a 20% premium on the 30-day VWAP, to terminate Nestlé Health Science’s director designation right if Nestlé Health Science ceases to own at least 10% of the outstanding shares of common stock, and to include a 12-month lock-up period. The members of the Transaction Committee advised that the Company should not sell its common stock below $1.00, which is the floor price set under the Company’s at-the-market sales program. Following the meeting, Mr. Shaff sent a revised MOU to Mr. Hendrix and representatives of Evercore.

Also on May 13, 2024, Mr. DesRosier had a phone call with Mr. Hendrix during which they reviewed the revised MOU and discussed the board designation right, Nestlé Health Science’s obligations to utilize the VOWST assets, and certain of the leases.

On May 15, 2024, Mr. Hendrix sent to Messrs. Shaff and DesRosier and representatives of Lazard a revised MOU which included a provision stating that Nestlé Health Science is not obligated to utilize the VOWST assets, clarifying the scope of lease obligations to be assumed by Nestlé Health Science, reducing the 30-day VWAP price per share premium from 20% to 10%, and reducing the lock-up period to 6 months.

On May 16, 2024, Mr. DesRosier and Mr. Hendrix had a phone call at which they discussed the scope of certain lease obligations to be assumed by Nestlé Health Science. Following that call, also on May 16, 2024, Mr. DesRosier sent a revised MOU to Mr. Hendrix and representatives of Evercore reflecting their conversation.

On May 16, 2024, Seres granted access to Nestlé Health Science to Seres’ virtual data room.

On May 17, 2024, representatives of Latham and representatives of Mayer Brown LLP, outside counsel to Nestlé Health Science (“Mayer Brown”), held a conference call and discussed the status of the MOU and Seres’ press release, as well as the definitive transaction agreements.

On May 23, 2024, Seres and Lazard entered into an engagement letter formalizing Lazard’s engagement to act as financial advisor to Seres in connection with the transaction. Lazard was engaged by Seres to assist with an analysis of the business and financial condition of the Company, to formulate strategy and structural alternatives, and in connection with negotiations and the consummation of the transaction. Seres engaged Lazard based on Lazard’s experience and reputation. Pursuant to its engagement by Seres, Lazard will be entitled to an aggregate fee of $3 million for its services, which is payable to Lazard upon the consummation of the transaction. Seres has also agreed to reimburse Lazard for certain expenses and to indemnify Lazard, its affiliates and certain related parties against certain liabilities and expenses, arising out of or related to Lazard’s engagement.

On June 5, 2024, Seres and Nestlé Health Science signed the MOU and representatives of Mayer Brown sent an initial draft of the Purchase Agreement to Latham.

Thereafter, during the period from June 5, 2024 through August 5, 2024, representatives of Seres and Nestlé Health Science and their respective legal advisors negotiated the terms of the Purchase Agreement and the other transaction documents. Key terms of the Purchase Agreement negotiated between the parties included, among other things: (i) the scope of the intellectual property and other assets to be acquired by Nestlé Health Science, (ii) whether and to what extent the development costs (including clinical studies costs) and regulatory expenses, payments to third parties in connection with third party license payments, and payments for amounts payable under the Transition Services Agreement would be included in Allowable Expenses (i.e., expenses that are a part of the 50/50 cost split), (iii) the treatment of the lease for Seres’ Waltham facility, (iv) the accounting treatment and reporting of Net Sales and other information rights of Seres during the Profit Sharing Period and during the Milestone Period, (v) the parameters regarding the conditionality of Seres’ receipt of the Installment Payments on Seres’ compliance with its obligations under the Transition Services Agreement, (vi) the conditions for termination of the Purchase Agreement, (vii) the circumstances in which Seres could change its recommendation regarding the proposed transaction, (viii) the amount of the expense reimbursement that Seres agreed to pay to Nestlé Health Science under certain circumstances of termination, and (ix) the post-closing indemnification obligations of each party, including the limitations thereof.

On June 6, 2024, Seres issued a press release publicly announcing the signing of the MOU.

On June 17, 2024, Seres and Houlihan Lokey entered into an engagement letter for Houlihan Lokey to provide an opinion to the Seres Board as to the fairness, from a financial point of view, to Seres of the aggregate consideration to be received by Seres in the transaction. Houlihan Lokey was engaged for this purpose because of its experience and reputation.

On July 30, 2024, the Transaction Committee met with members of Seres management to discuss the terms of the Purchase Agreement and the other transaction documents. Based on these discussions, the Transaction Committee advised management on negotiations with Nestlé Health Science.

On August 4, 2024, at a special meeting of the Seres Board held to discuss the latest developments with respect to the transaction with Nestlé Health Science, the Seres Board reviewed the overall sale process. Representatives of Latham reviewed with the Seres Board its fiduciary duties under Delaware law in evaluating the proposed transaction. Seres management and representatives of Latham then provided an overview of the negotiations with Nestlé Health Science and summarized key terms of the proposed Purchase Agreement, such as the termination fee, the closing conditions and deliverables, and the survival of indemnification obligations. Representatives of

Latham and members of management updated the Seres Board with respect to the expected timing and conditions to closing (and potential exposure and related risks), post-closing transition services and related matters. Also at this meeting, representatives of Houlihan Lokey reviewed their preliminary financial analysis of the Company and the Transaction Consideration with the Seres Board.

From August 4, 2024 through August 5, 2024, representatives of Latham and Mayer Brown worked together to finalize the remaining outstanding issues in the Purchase Agreement and other remaining transaction documents.

On August 5, 2024, a special meeting of the Audit Committee of the Seres Board was held to discuss the related party transaction with Nestlé Health Science. At the meeting, the Audit Committee determined, among other things, that the proposed transaction with Nestlé Health Science does not create or constitute a “conflict of interest” under the Company’s Code of Business Conduct and Ethics.

On August 5, 2024, at a special meeting of the Seres Board held to discuss the latest developments with respect to the transaction with Nestlé Health Science, the Seres Board again reviewed the overall sale process as conducted to date. Seres management and representatives of Latham then provided an overview of the resolution of outstanding open points thereunder, such as the treatment of the Bacthera Agreement. Also at this meeting, representatives of Houlihan Lokey rendered an oral opinion, confirmed by delivery of a written opinion dated August 5, 2024, to the Seres Board to the effect that, as of that date and based on and subject to various assumptions made, procedures followed, matters considered and limitations and qualifications on the review undertaken by Houlihan Lokey, the Transaction Consideration to be received by the Company for the Acquired Assets subject to the Assumed Liabilities in the Transaction pursuant to the Purchase Agreement was fair, from a financial point of view, to the Company.

After carefully considering the various factors described under the section captioned “— Recommendation of the Seres Board and Reasons for the Transaction,” the Seres Board unanimously approved entry into the Purchase Agreement.

On August 5, 2024, the Company executed the Purchase Agreement with Nestlé Health Science and issued a press release announcing the sale of VOWST.

In evaluating the Purchase Agreement and the Transaction, the Seres Board consulted with Seres management and its financial and legal advisors and unanimously determined the terms of the Purchase Agreement and the transactions contemplated thereby were advisable and in the best interests of Seres and its stockholders and resolved to recommend that stockholders vote to approve the Transaction. In reaching this determination, the Seres Board considered a variety of factors, including the following:

In evaluating the Purchase Agreement and the Transaction, the Seres Board consulted with Seres management and its financial and legal advisors, and also considered a variety of risks and other potentially negative factors relating to the Purchase Agreement and the Transaction, including the following:

The Seres Board determined that overall, these potential risks and uncertainties are outweighed by the benefits that the Seres Board expects to achieve for Seres as a result of the Transaction.

The foregoing description of the factors considered by the Seres Board is not intended to be exhaustive, but rather includes material factors considered by the Seres Board. The Seres Board also considered other factors in reaching its unanimous determination that the Purchase Agreement and the transactions contemplated thereby were advisable and in the best interests of Seres and its stockholders, and resolving to recommend that stockholders vote to approve the Transaction. In reaching its decision and recommendation, the Seres Board did not quantify or assign any relative weights to the factors considered and individual directors may have given different weights to different factors.

The foregoing discussion of the information and factors considered by the Seres Board is forward-looking in nature. This information should be read in light of the factors set forth in the section entitled “Cautionary Statement Regarding Forward-Looking Statements.”

On August 5, 2024, Houlihan Lokey orally rendered its opinion to the Seres Board (which was subsequently confirmed in writing by delivery of Houlihan Lokey’s written opinion addressed to the Seres Board dated August 5, 2024), as to whether, as of such date, the Transaction Consideration to be received by Seres in exchange for the Acquired Assets subject to the Assumed Liabilities in the Transaction pursuant to the Purchase Agreement was fair, from a financial point of view, to Seres.

Houlihan Lokey’s opinion was directed to the Seres Board (in its capacity as such) and only addressed whether the Transaction Consideration to be received by Seres in exchange for the Acquired Assets subject to the Assumed Liabilities in the Transaction pursuant to the Purchase Agreement was fair, from a financial point of view, to Seres and did not address any other aspect or implication of the Transaction or any other agreement, arrangement or understanding. The summary of Houlihan Lokey’s opinion in this proxy statement is qualified in its entirety by reference to the full text of its written opinion, which is attached as Annex B to this proxy statement and describes the procedures followed, assumptions made, qualifications and limitations on the review undertaken and other matters considered by Houlihan Lokey in connection with the preparation of its opinion. However, neither Houlihan Lokey’s opinion nor the summary of its opinion and the related analyses set forth in this proxy statement are intended to be, and do not constitute, advice or a recommendation to the Seres Board, any security holder or any other person as to how to act or vote with respect to any matter relating to the Transaction or otherwise.

In connection with its opinion, Houlihan Lokey made such reviews, analyses and inquiries as Houlihan Lokey deemed necessary and appropriate under the circumstances. Among other things, Houlihan Lokey:

Houlihan Lokey relied upon and assumed, without independent verification, the accuracy and completeness of all data, material and other information furnished, or otherwise made available, to it, discussed with or reviewed by it, or publicly available, and did not assume any responsibility with respect to such data, material and other information. Management of Seres advised Houlihan Lokey, and at Seres’ direction, Houlihan Lokey relied upon and assumed, that the Seres Liquidation Analysis was reasonably prepared by the management of Seres in good faith on bases reflecting the best currently available estimates and judgments of such management as to the expected realizable value for Seres’ assets in a liquidation of such assets and the amounts, if any, estimated to be available for distribution to the holders of Seres common stock. In particular, management of Seres advised Houlihan Lokey, and at Seres’ direction Houlihan Lokey relied upon and assumed, that as set forth in the Seres Liquidation Analysis, Seres’ intellectual property related to SER-155 was expected to have no realizable value in a liquidation of Seres’ assets. At Seres’ direction, Houlihan Lokey relied, without independent verification, solely upon the judgment of the management of Seres regarding all aspects of the Seres Liquidation Analysis. In addition, management of Seres advised Houlihan Lokey, and at Seres’ direction, Houlihan Lokey relied upon and assumed, that (i) the VOWST Net Sales Projections were reasonably prepared in good faith on bases reflecting the best currently available estimates and judgments of such management as to the future net sales of the Product, assuming, for illustrative purposes, Seres would have sufficient capital to operate on a standalone basis in accordance with Seres business plan underlying such projections, (ii) the VOWST Net Sales Projections could not be achieved in the absence of the Transaction, and (iii) the Profit Sharing Period Projections were reasonably prepared in good faith on bases reflecting the best currently available estimates and judgments of such management as to the amounts payable or receivable by Seres pursuant to the Profit Sharing Arrangement, the MSK Costs, the Ongoing Safety Study Expenses and the Lease Expenses. At Seres’ direction, Houlihan Lokey assumed that the Seres Liquidation Analysis provided a reasonable basis on which to evaluate Seres, the VOWST Net Sales Projections provided a reasonable basis on which to evaluate the Milestone Payments, and the Profit Sharing Period Projections provided a reasonable basis on which to evaluate the Profit Sharing Arrangement, the MSK Costs, the Ongoing Safety Study Expenses and the Lease Expenses. In addition, Houlihan Lokey, at Seres’ direction, used and relied upon the Seres Liquidation Analysis, the VOWST Net Sales Projections and the Profit Sharing Period Projections for purposes of Houlihan Lokey’s analyses and opinion. Houlihan Lokey expressed no view or opinion with respect to the Seres Liquidation Analysis, the VOWST Net Sales Projections, the Profit Sharing Period Projections or the respective assumptions on which they were based. If the assumptions, estimates or conclusions set forth in the Seres Liquidation Analysis, the VOWST Net Sales Projections or the Profit Sharing Period Projections are not accurate, the conclusions set forth in Houlihan Lokey’s opinion could be materially affected.

Management of Seres advised Houlihan Lokey, and at Seres’ direction Houlihan Lokey relied upon and assumed, that (i) Seres had identified conditions and events that raise substantial doubt regarding Seres’ ability to continue as a going concern, (ii) Seres had implemented a restructuring plan that included (a) a reduction of Seres’ workforce by approximately 41% across the organization, resulting in the elimination of approximately

160 positions, (b) a significant scaling back of all non-partnered research and development activities other than the completion of Seres’ SER-155 Phase 1b study, and (c) a reduction of general and administrative expenses, including consolidating office space, (iii) Seres had incurred net losses and negative cashflows since its inception and, despite its restructuring plan, Seres expected that its operating losses and negative cash flows would continue for the foreseeable future, (iv) based on Seres’ currently available cash resources, current and forecasted level of operations, and forecasted cash flows, Seres would require additional funding for its operations, (v) substantial doubt about Seres’ ability to continue as a going concern could materially and adversely affect the price per share of Seres common stock, could make it more difficult for Seres to obtain financing, and could cause potential collaborators to decline to do business with Seres, (vi) Seres had been unsuccessful in obtaining additional financing on terms acceptable to it, (vii) Seres received a notice of default under the Oaktree Credit Agreement, (viii) upon the occurrence of certain events of default under the Oaktree Credit Agreement, Oaktree Fund Administration, LLC, as administrative agent, would be entitled to cause Seres’ indebtedness thereunder to become immediately due and payable, and to exercise other remedies against Seres and the collateral securing the loan, including cash, (ix) Seres’ failure to conclude the Transaction or an alternative strategic transaction would force it to consider other strategic alternatives such as liquidation and dissolution, and (x) the values Seres receives for its assets in liquidation or dissolution could be significantly lower than the values reflected in Seres’ financial statements, and would be materially less than the Transaction Consideration to be received by Seres in the Transaction.

Houlihan Lokey relied upon and assumed, without independent verification, that there had been no change in the businesses, assets, liabilities, financial condition, results of operations, cash flows or prospects of Seres since the respective dates of the most recent financial statements and other information, financial or otherwise, provided to Houlihan Lokey that would be material to its analyses or opinion, and that there was no information or any facts that would make any of the information reviewed by Houlihan Lokey incomplete or misleading. In reaching its conclusions in the opinion, with Seres’ consent and approval, (i) Houlihan Lokey did not rely upon a discounted cash flow analysis of Seres, due to the substantial doubt of Seres management about Seres’ ability to continue as a going concern and the fact that, as Seres advised Houlihan Lokey and directed Houlihan Lokey to assume, Seres projected that it would exhaust its cash prior to December 31, 2024, and (ii) Houlihan Lokey did not rely upon a review of the publicly available financial terms of other transactions or a review of other companies with publicly traded equity securities, due to the substantial doubt of the management of Seres about Seres’ ability to continue as a going concern. In addition, for purposes of its analyses and opinion, Houlihan Lokey, with Seres’ consent and approval, assumed that (i) the Acquired Assets included all of the assets or rights necessary and sufficient to achieve the Seres projections for the Product subject to the Assumed Liabilities in the amounts and at the times contemplated thereby, (ii) the Acquired Assets did not include any assets or rights that Seres or any of its affiliates would require to exploit any other products or potential products of Seres being retained by Seres and its affiliates in the Transaction (the “Retained Products”), to perform Seres’ obligations under the Transition Services Agreement or the Cross-License Agreement to be entered into between Seres and Purchaser in connection with the Transaction, or to own or operate any other businesses or operations of Seres or such affiliates (the “Retained Businesses”) as currently conducted or as contemplated by Seres and its affiliates could be conducted by Seres and its affiliates in the future, (iii) upon the consummation of the Transaction, neither Seres nor any of its affiliates would retain or otherwise be responsible for the Assumed Liabilities and (iv) the Transaction would not otherwise impair the ability of Seres and its affiliates to exploit any Retained Products, to perform Seres’ obligations under the Transition Services Agreement or the Cross-License Agreement, or to own and operate the Retained Businesses as currently conducted, or as contemplated by management of Seres and its affiliates could be conducted in the future.

Houlihan Lokey relied upon and assumed, without independent verification, that (a) the representations and warranties of all parties to the Purchase Agreement and all other related documents and instruments referred to therein were true and correct, (b) each party to the Purchase Agreement and such other related documents and instruments would fully and timely perform all of the covenants and agreements required to be performed by such party, (c) all conditions to the consummation of the Transaction would be satisfied without waiver thereof, and (d) the Transaction would be consummated in a timely manner in accordance with the terms described in the Purchase Agreement and such other related documents and instruments, without any amendments or modifications thereto. Houlihan Lokey relied upon and assumed, without independent verification, that (i) the Transaction would be consummated in a manner that complies in all respects with all applicable foreign, federal, state and local statutes, rules and regulations, and (ii) all governmental, regulatory and other consents and

approvals necessary for the consummation of the Transaction would be obtained and that no delay, limitations, restrictions or conditions would be imposed or amendments, modifications or waivers made that would have an effect on the Transaction the Product, Seres or SPN or any expected benefits of the Transaction that would be material to Houlihan Lokey’s analyses or its opinion. Houlihan Lokey also relied upon and assumed, without independent verification, at Seres’ direction, that any adjustments to the Transaction Consideration pursuant to the Purchase Agreement or otherwise would not be material to Houlihan Lokey’s analyses or opinion. In addition, Houlihan Lokey relied upon and assumed, without independent verification, that the final form of the Purchase Agreement would not differ in any respect from the draft of the Purchase Agreement identified above.

Furthermore, in connection with its opinion, Houlihan Lokey was not requested to, and did not, make any physical inspection or independent appraisal or evaluation of any of the assets, properties or liabilities (fixed, contingent, derivative, off-balance-sheet or otherwise) of Seres, SPN or any other party, nor was Houlihan Lokey provided with any such appraisal or evaluation (other than the Seres Liquidation Analysis provided by Seres management). Houlihan Lokey did not estimate, and expressed no opinion regarding, the liquidation value of any entity or business. Houlihan Lokey did not undertake any independent analysis of any potential or actual litigation, regulatory action, possible unasserted claims or other contingent liabilities, to which the Product, Seres or SPN was or may have been a party or was or may have been subject, or of any governmental investigation of any possible unasserted claims or other contingent liabilities to which the Product, Seres or SPN was or may have been a party or was or may have been subject.

Houlihan Lokey was not requested to, and did not, (a) initiate or participate in any discussions or negotiations with, or solicit any indications of interest from, third parties with respect to the Transaction, the securities, assets, business or operations of Seres or any other party, or any alternatives to the Transaction, (b) negotiate the terms of the Transaction, (c) advise the Seres Board, Seres or any other party with respect to alternatives to the Transaction, or (d) identify, introduce to Seres or any other party, or screen for creditworthiness, any prospective investors, lenders or other participants in the Transaction.

Houlihan Lokey’s opinion was necessarily based on financial, economic, market and other conditions as in effect on, and the information made available to Houlihan Lokey as of, the date of its opinion. Houlihan Lokey did not undertake, and was under no obligation, to update, revise, reaffirm or withdraw its opinion, or otherwise comment on or consider events occurring or coming to Houlihan Lokey’s attention after the date of its opinion. Houlihan Lokey did not express any opinion as to the price or range of prices at which Seres common stock could be purchased or sold, or otherwise be transferable, at any time.

Houlihan Lokey’s opinion was furnished for the use of the Seres Board (in its capacity as such) in connection with its evaluation of the Transaction and may not be used for any other purpose without Houlihan Lokey’s prior written consent. Houlihan Lokey’s opinion was not intended to be, and did not constitute, a recommendation to the Seres Board, Seres, any security holder or any other party as to how to act or vote with respect to any matter relating to the Transaction or otherwise.

Houlihan Lokey was not requested to opine as to, and its opinion did not express an opinion as to or otherwise address, among other things: (i) the underlying business decision of the Seres Board, Seres, its security holders or any other party to proceed with or effect the Transaction, (ii) the terms of any arrangements, understandings, agreements or documents related to, or the form, structure or any other portion or aspect of, the Transaction or otherwise (other than the Transaction Consideration to the extent expressly specified in its opinion), including, without limitation, the support agreements to be entered into in connection with the Transaction, the Securities Purchase Agreement, the Transition Services Agreement, the Cross-License Agreement or the respective transactions contemplated thereby, (iii) the fairness of any portion or aspect of the Transaction to the holders of any class of securities, creditors or other constituencies of Seres, SPN, or to any other party, (iv) the relative merits of the Transaction as compared to any alternative business strategies or transactions that might have been available for Seres, SPN or any other party, (v) the fairness of any portion or aspect of the Transaction to any one class or group of Seres’, SPN’s or any other party’s security holders or other constituents vis-à-vis any other class or group of Seres’, SPN’s or such other party’s security holders or other constituents (including, without limitation, the allocation of any consideration amongst or within such classes or groups of security holders or other constituents), (vi) whether or not Seres, SPN, their respective security holders or any other party is receiving or paying reasonably equivalent value in the Transaction, (vii) the solvency, creditworthiness or fair value of Seres, SPN or any other participant in the Transaction, or any of their respective assets, under any applicable laws relating to bankruptcy, insolvency, fraudulent conveyance or similar matters, or (viii) the fairness,

financial or otherwise, of the amount, nature or any other aspect of any compensation to or consideration payable to or received by any officers, directors or employees of any party to the Transaction, any class of such persons or any other party, relative to the Transaction Consideration or otherwise. Furthermore, Houlihan Lokey did not express any opinion, counsel or interpretation regarding matters that require legal, environmental, regulatory, accounting, insurance, tax or other similar professional advice. Houlihan Lokey assumed that such opinions, counsel or interpretations had been or would be obtained from the appropriate professional sources. Furthermore, Houlihan Lokey relied, with the consent of the Seres Board, on the assessments by the Seres Board, Seres, SPN and their respective advisors, as to all legal, environmental, regulatory, accounting, insurance, tax and other similar matters with respect to the Product, Seres, SPN and the Transaction or otherwise.

In performing its analyses, Houlihan Lokey considered general business, economic, industry and market conditions, financial and otherwise, and other matters as they existed on, and could be evaluated as of, the date of its opinion. No company, transaction or business used in Houlihan Lokey’s analyses for comparative purposes is identical to Seres or the proposed Transaction and an evaluation of the results of those analyses is not entirely mathematical. The estimates contained in the Seres projections for the Product and the Profit Sharing Period Projections and the implied reference range values indicated by Houlihan Lokey’s analyses are not necessarily indicative of actual values or predictive of future results or values, which may be significantly more or less favorable than those suggested by the analyses. In addition, any analyses relating to the value of assets, businesses or securities do not purport to be appraisals or to reflect the prices at which businesses or securities actually may be sold, which may depend on a variety of factors, many of which are beyond the control of Seres. Much of the information used in, and accordingly the results of, Houlihan Lokey’s analyses are inherently subject to substantial uncertainty.

Houlihan Lokey’s opinion was only one of many factors considered by the Seres Board in evaluating the proposed Transaction. Neither Houlihan Lokey’s opinion nor its analyses were determinative of the Transaction Consideration or of the views of the Seres Board or management with respect to the Transaction or the adequacy of the Transaction Consideration. Under the terms of its engagement by Seres, neither Houlihan Lokey’s opinion nor any other advice or services rendered by it in connection with the proposed Transaction or otherwise, should be construed as creating, and Houlihan Lokey should not be deemed to have, any fiduciary duty to, or agency relationships with, the Seres Board, Seres, SPN, any security holder or creditor of Seres, SPN or any other person, regardless of any prior or ongoing advice or relationships. The type and amount of consideration payable in the Transaction were determined through negotiation between Seres and SPN, and the decision to enter into the Purchase Agreement was solely that of the Seres Board.

The following is a summary of the material financial analyses considered by Houlihan Lokey in connection with the preparation of its opinion and reviewed with the Seres Board on August 5, 2024. The summary of these analyses is not a complete description of the analyses underlying Houlihan Lokey’s opinion. The preparation of such an opinion is a complex process involving various quantitative and qualitative judgments and determinations with respect to the financial, comparative and other analytical methods employed and the adaptation and application of these methods to the unique facts and circumstances presented. As a consequence, neither Houlihan Lokey’s opinion nor the underlying analyses are readily susceptible to summary description. Houlihan Lokey arrived at its opinion based on the results of all reviews undertaken by it and assessed as a whole and did not draw, in isolation, conclusions from or with regard to any individual analysis, methodology or factor.

In reaching its conclusions in its opinion, (i) Houlihan Lokey did not rely upon a discounted cash flow analysis of Seres, due to the substantial doubt of Seres management about Seres’ ability to continue as a going concern and the fact that, as Seres advised Houlihan Lokey and directed Houlihan Lokey to assume, Seres projected that it would exhaust its cash prior to December 31, 2024, and (ii) Houlihan Lokey did not rely upon a review of the publicly available financial terms of other transactions or a review of other companies with publicly traded equity securities, due to the substantial doubt of the management of Seres about Seres’ ability to continue as a going concern.

Review of the Transaction Consideration. Houlihan Lokey calculated an implied value reference range for the Transaction Consideration to be received by Seres in exchange for the Acquired Assets subject to the Assumed Liabilities in the Transaction pursuant to the Purchase Agreement based on the total upfront consideration of $100 million (to be received at closing), the second installment payment of $50 million (to be received on

January 15, 2025) and the third installment payment of $25 million (to be received on July 1, 2025), and estimates provided by Seres of other cash flow items comprised of (i) intercompany account settlement liabilities of $17.9 million (payable at closing), (ii) certain liabilities retained by Seres under the Bacthera Agreement of $2.3 million (payable at closing) and (iii) certain liabilities related to employment related payments of $1.5 million (payable on July 1, 2025). The second and third installment payments and estimated liabilities related to employment related payments were discounted to present value using a discount rate of 4.7%, which resulted in an aggregate implied value of the upfront payment and installment payments, adjusted for such cash flow items as provided by Seres management, of $151.9 million. Houlihan Lokey also calculated the implied net present value of the Milestone Payments, net of accrued interest on the Prepaid Milestone, based on the Seres projections for the Product, and the amounts payable or receivable by Seres pursuant to the Profit Sharing Arrangement, the MSK Costs, the Ongoing Safety Study Expenses and the Lease Expenses, based on the Profit Sharing Period Projections. Houlihan Lokey applied discount rates ranging from 13.5% to 14.5%, which resulted in an implied aggregate value reference range for the Milestone Payments, net of accrued interest on the Prepaid Milestone, of $100.7 million to $106.1 million and an implied aggregate value reference range for the amounts payable by Seres pursuant to the Profit Sharing Arrangement, the MSK Costs, the Ongoing Safety Study Expenses and the Lease Expenses of $43.6 million to $43.9 million. Taking into account (i) the aggregate implied value of the upfront payment and installment payments to be received by Seres, adjusted for the cash flow items as provided by management of Seres, (ii) the implied aggregate value reference range for the Milestone Payments, net of accrued interest on the Prepaid Milestone, to be received by Seres, and (iii) the implied aggregate value reference range for the amounts payable by Seres pursuant to the Profit Sharing Arrangement, the MSK Costs, the Ongoing Safety Study Expenses and the Lease Expenses, the review of the Transaction Consideration resulted in an implied value reference range for the Transaction Consideration to be received by Seres in exchange for the Acquired Assets subject to the Assumed Liabilities in the Transaction pursuant to the Purchase Agreement ranging from $208.6 million to $214.3 million.

Review of Liquidation Analysis. Houlihan Lokey reviewed and considered the Seres Liquidation Analysis, which was prepared by the management of Seres and is described in this proxy statement under the heading, “—Seres Liquidation Analysis.” The Seres Liquidation Analysis estimated the potential realizable values for Seres’ assets in a liquidation and the remaining amounts, if any, available upon completion of such liquidation for distribution to holders of Seres common stock. Houlihan Lokey noted that the Seres Liquidation Analysis estimated a range of potential realizable values for Seres’ assets in a liquidation of $99.5 million to $118.4 million, a range of liabilities of $177.5 million to $189.2 million, and a range of liquidation costs of $48.8 million to $62.4 million, which resulted in a hypothetical liquidation value reference range for Seres of approximately negative $152 million to negative $107.8 million. The Seres Liquidation Analysis assumed SPN, given its prior collaboration with Seres and its existing license regarding VOWST, would potentially acquire the VOWST business in such a liquidation for an amount, in excess of the liquidation value of the assets, ranging from $86.3 million to $107.8 million (which assumed a repayment ranging from 80% to 100% of the net liabilities remaining after a liquidation), which resulted in a hypothetical liquidation value reference range for Seres of negative $65.8 million to $0.00, as compared to the implied value reference range of the Transaction Consideration to be received by Seres in exchange for the Acquired Assets subject to the Assumed Liabilities in the Transaction pursuant to the Purchase Agreement ranging from $208.6 million to $214.3 million.

Houlihan Lokey was engaged by Seres to provide an opinion to the Seres Board as to the fairness, from a financial point of view, of the Transaction Consideration to be received by Seres in exchange for the Acquired Assets subject to the Assumed Liabilities in the Transaction pursuant to the Purchase Agreement. Seres engaged Houlihan Lokey based on Houlihan Lokey’s experience and reputation. Houlihan Lokey is regularly engaged to render financial opinions in connection with mergers, acquisitions, divestitures, leveraged buyouts, and for other purposes. Pursuant to its engagement by Seres, Houlihan Lokey became entitled to an aggregate fee of $500,000 for its services, a portion of which became payable to Houlihan Lokey upon its retention by Seres and the remainder of which became payable upon the delivery of Houlihan Lokey’s opinion to the Seres Board. No portion of Houlihan Lokey’s fee is contingent upon the successful completion of the Transaction. Seres has also agreed to reimburse Houlihan Lokey for certain expenses and to indemnify Houlihan Lokey, its affiliates and certain related parties against certain liabilities and expenses, including certain liabilities under the federal securities laws, arising out of or related to Houlihan Lokey’s engagement.

In the ordinary course of business, certain of Houlihan Lokey’s employees and affiliates, as well as investment funds in which they may have financial interests or with which they may co-invest, may acquire, hold or sell, long or short positions, or trade, in debt, equity, and other securities and financial instruments (including loans and other obligations) of, or investments in, Seres, SPN or any other party that may be involved in the Transaction and their respective affiliates or security holders or any currency or commodity that may be involved in the Transaction.

Houlihan Lokey and/or certain of its affiliates have in the past provided investment banking, financial advisory and/or other services to Flagship, or one or more security holders or affiliates of, and/or portfolio companies of investment funds affiliated or associated with, Flagship (collectively, with Flagship, the “Flagship Group”) and have in the past provided and are currently providing investment banking, financial advisory and/or other financial or consulting services to Oaktree Capital Management, L.P. (“Oaktree”), or one or more security holders or affiliates of, and/or portfolio companies of investment funds affiliated or associated with, Oaktree (collectively, with Oaktree, the “Oaktree Group”), for which Houlihan Lokey and its affiliates have received, and may receive, compensation. Based on a review of its information management systems, Houlihan Lokey identified engagements during the two years prior to the date of its opinion with members of the Flagship Group for which Houlihan Lokey and/or its affiliates received aggregate compensation of approximately $3 million and with members of the Oaktree Group for which Houlihan Lokey and/or its affiliates received aggregate compensation of approximately $62 million, including, among other things, (i) having acted as exclusive placement agent and financial advisor to Indigo Ag, a member of the Flagship Group, in connection with a growth equity investment, which closed in 2023, (ii) having acted as financial advisor to the special committee of the board of directors of Oaktree Specialty Lending Corporation, which is managed by a member of the Oaktree Group, in connection with its merger transaction with Oaktree Strategic Income II, Inc., which closed in January 2023, (iii) having acted as financial advisor to a lender group, of which one or more members of the Oaktree Group were members, in relation to their interests as lenders to Samarco Mineração S.A. in connection with its restructuring transaction, which was completed in December 2023, (iv) having acted as financial advisor to a lender group, of which one or more members of the Oaktree Group were members, in relation to their interests as lenders to SiO2 Medical Products, Inc. in connection with its chapter 11 bankruptcy proceedings, which concluded in September 2023, (v) having acted as financial advisor to a lender group, of which one or more members of the Oaktree Group were members, in relation to their interests as lenders to CURO Group Holdings Corp. in connection with its chapter 11 bankruptcy proceedings, which concluded in May 2024, (vi) having acted as investment banker to Salem Harbor Power Development LP, then a member of the Oaktree Group, in connection with its chapter 11 bankruptcy proceedings, which concluded in August 2023, (vii) having acted as exclusive placement agent to Oaktree in connection with its financing of Electro Rent Corporation, which closed in December 2023, (viii) having acted as financial advisor to members of the Oaktree Group in connection with the acquisition of Aqseptence Group, which closed in November 2023, (ix) having acted as financial advisor to Aludyne, Inc., a member of the Oaktree Group, in connection with its refinancing transaction, which closed in March 2023 and another transaction which closed in April 2024, and (x) having acted as financial advisor to David’s Bridal, then a member of the Oaktree Group, in connection with its chapter 11 bankruptcy proceedings, which concluded in July 2023. In addition, in the course of its review, Houlihan Lokey also identified certain current engagements with one or more members of the Oaktree Group unrelated to the Transaction for which Houlihan Lokey and/or its affiliates could potentially receive, in the upcoming year, aggregate compensation of $5 million or more. Houlihan Lokey and certain of its affiliates may provide investment banking, financial advisory and/or other financial or consulting services to Seres, SPN, members of the Flagship Group, members of the Oaktree Group, other participants in the Transaction or certain of their respective affiliates or security holders in the future, for which Houlihan Lokey and its affiliates may receive compensation. In addition, Houlihan Lokey and certain of its affiliates and certain of Houlihan Lokey’s and its affiliates’ respective employees may have committed to invest in private equity or other investment funds managed or advised by Flagship, Oaktree, other participants in the Transaction or certain of their respective affiliates or security holders, and in portfolio companies of such funds, and may have co-invested with members of the Flagship Group, members of the Oaktree Group, other participants in the Transaction or certain of their respective affiliates or security holders, and may do so in the future. Furthermore, in connection with bankruptcies, restructurings, distressed situations and similar matters, Houlihan Lokey and certain of its affiliates may have in the past acted, may currently be acting and may in the future act as financial advisor to debtors, creditors, equity holders, trustees, agents and other interested parties (including, without limitation, formal and informal committees or groups of creditors) that may have included or represented and

may include or represent, directly or indirectly, or may be or have been adverse to, Seres, SPN, members of the Flagship Group, members of the Oaktree Group, other participants in the Transaction or certain of their respective affiliates or security holders, for which advice and services Houlihan Lokey and its affiliates have received and may receive compensation.

In connection with the evaluation of the Transaction by the Seres Board, Seres management prepared and presented an analysis regarding a potential liquidation of Seres (the “Seres Liquidation Analysis”) as a potential alternative to the transaction with SPN.

The inclusion of the Seres Liquidation Analysis should not be deemed an admission or representation by Seres or any of its officers, directors, affiliates, advisors, or other representatives with respect to the Seres Liquidation Analysis. The liquidation analysis is not included to influence your views on the Transaction, the Purchase Agreement and the transactions contemplated thereby and is summarized in this proxy statement solely to provide stockholders access to certain information considered by the Seres Board in connection with its evaluation of the Transaction, the Purchase Agreement and the transactions contemplated thereby and provided to Houlihan Lokey, who was authorized and directed to rely upon the Seres Liquidation Analysis for purposes of its opinion to the Seres Board. Any estimates contained in the Seres Liquidation Analysis are not necessarily indicative of actual values or predictive of future results or values, which could have been significantly more or less favorable than as set forth below. In addition, analyses relating to the liquidation value of Seres do not purport to be appraisals or reflect the prices at which Seres common stock may actually be valued or traded. The assumptions and estimates used in, and the results derived from, the Seres Liquidation Analysis are hypothetical, and are thus, inherently subject to substantial uncertainty.

The Seres Liquidation Analysis was not prepared with a view toward compliance with published guidelines of the SEC regarding projections and forward-looking statements or the guidelines established by the American Institute of Certified Public Accountants for preparation and presentation of prospective financial information. The Seres Liquidation Analysis included in this document has been prepared by, and is the responsibility of, Seres management. PricewaterhouseCoopers LLP has not audited, reviewed, examined, compiled nor applied agreed-upon procedures with respect to the accompanying Seres Liquidation Analysis and, accordingly, PricewaterhouseCoopers LLP does not express an opinion or any other form of assurance with respect thereto. The PricewaterhouseCoopers LLP report incorporated by reference to our Current Report on Form 8-K filed on August 15, 2024, relates to Seres’ previously issued financial statements. It does not extend to the Seres Liquidation Analysis and should not be read to do so.

The Seres Liquidation Analysis includes estimates of cash and of certain expenditures, which for the purpose of the Seres Liquidation Analysis were not calculated in accordance with GAAP. Non-GAAP financial measures should not be viewed as a substitute for GAAP financial measures and may be different from non-GAAP financial measures used by other companies. Furthermore, there are limitations inherent in non-GAAP financial measures because they exclude charges and credits that are required to be included in a GAAP presentation. Accordingly, non-GAAP financial measures should be considered together with, and not as an alternative to, financial measures prepared in accordance with GAAP. The SEC rules, which otherwise would require a reconciliation of a non-GAAP financial measure to a GAAP financial measure, do not apply to non-GAAP financial measures provided to a board of directors or financial advisors in connection with a proposed business combination transaction such as the Transaction if the disclosure is included in a document such as this proxy statement to comply with requirements under state laws, including case law.

The Seres Liquidation Analysis speaks only as to the date on which it was generated, and Seres undertakes no obligation to update or otherwise revise or reconcile the Seres Liquidation Analysis to reflect circumstances existing after the date the Seres Liquidation Analysis was generated or to reflect the occurrence of future events. Seres does not intend to make publicly available any update or other revisions to the liquidation analysis, except as otherwise required by law. In light of the foregoing factors and the uncertainties inherent in estimated cash balances, stockholders are cautioned not to place undue reliance, if any, on the Seres Liquidation Analysis.

The Seres Liquidation Analysis does not account for potential liabilities of Seres that cannot be reasonably estimated or quantified, including potential risks and uncertainties associated with pursuing a winding down and liquidation of Seres. Such liabilities could materially affect the cash amounts that, in the event of a liquidation or dissolution of Seres, may be distributed to stockholders as permitted under applicable law.

The below summary is included solely to give stockholders access to the Seres Liquidation Analysis evaluated by the Seres Board, and is not included in this proxy statement to influence a stockholder’s decision whether or not to vote for the proposals, or for any other purposes.

The Seres Liquidation Analysis estimated the potential realizable values for Seres’ assets in a liquidation and the remaining amounts, if any, available upon completion of such liquidation for distribution to holders of Seres common stock. The Seres Liquidation Analysis assumed (i) SPN, given its prior collaboration with Seres and its existing license for VOWST, would potentially acquire the VOWST business in such a liquidation and (ii) Seres would maintain critical vendors, key employees and its supply chain in order to operate the business as a going concern for approximately three months.

Seres does not, as a matter of course, publicly disclose internal projections of its future financial performance, revenue, earnings or other results due to, among other reasons, the unpredictability and uncertainty of the underlying assumptions and estimates. In connection with discussions regarding the proposed Transaction, Seres management provided certain unaudited prospective financial information (the “Projections”) to the Seres Board in connection with its evaluation of the Transaction and to representatives of Houlihan Lokey. The Projections consisted of (i) certain unaudited prospective net sales information for the VOWST Business (the “VOWST Net Sales Projections”) and (ii) Profit Sharing Period Projections consisting of estimates of the amounts payable by Seres pursuant to the Profit Sharing Payments, royalty and milestone payments under the MSK Agreement during the Profit Sharing Period, costs and expenses incurred in connection with the conduct of the VOWST safety study (the “Ongoing Safety Study Expenses”) during the Profit Sharing Period and 80.1% of all rent and other costs due to the landlord under the lease for Seres’ Waltham facility with respect to the Profit Sharing Period (the “Lease Expenses”). The VOWST Net Sales

Projections reflect a risk-adjusted outlook and were based on certain assumptions about the future financial performance of VOWST, including the commercialization of VOWST, sales ramp, pricing, reimbursement, market size, market share, competition, contractual relationships and other relevant factors relating to the VOWST Business. The VOWST Net Sales Projections assume, for illustrative purposes, Seres would have sufficient capital to operate on a standalone basis in accordance with its business plan. The Seres Board directed Houlihan Lokey to use the VOWST Net Sales Projections solely for purposes of evaluating the Milestone Payments, and to use the Profit Sharing Period Projections solely for purposes of evaluating the expected costs to Seres from the Profit Sharing Arrangement, the MSK Costs, the Ongoing Safety Study Expenses and the Lease Expenses.

The following table sets forth the VOWST Net Sales Projections provided to the Seres Board in connection with its evaluation of the Transaction and to representatives of Houlihan Lokey for use in connection with its financial analyses and its opinion as described in the section “—Opinion of Houlihan Lokey”:

“Net Sales” includes revenue contributions from specialty pharmacy, specialty distributors, and inventory.

The VOWST Net Sales Projections were based on numerous variables and assumptions, including the following key assumptions:

The following table sets forth the Profit Sharing Period Projections provided to the Seres Board in connection with its evaluation of the Transaction and to representatives of Houlihan Lokey for use in connection with its financial analyses and its opinion as described in the section “—Opinion of Houlihan Lokey”:

The Projections were not prepared with a view toward public disclosure and the summary thereof is included in this proxy statement only because such information was made available as described above. The Projections were not prepared with a view toward compliance with the published guidelines of the SEC regarding projections and forward-looking statements or the guidelines established by the American Institute of Certified Public Accountants for preparation or presentation of prospective financial information. The Projections included in this document have been prepared by, and are the responsibility of, Seres management. PricewaterhouseCoopers LLP has not audited, reviewed, examined, compiled nor applied agreed-upon procedures with respect to the accompanying Projections and, accordingly, PricewaterhouseCoopers LLP does not express an opinion or any other form of assurance with respect thereto. The PricewaterhouseCoopers LLP report incorporated by reference to our Current Report on Form 8-K filed on August 15, 2024 relates to Seres’ previously issued financial statements. It does not extend to the Projections and should not be read to do so. The Projections were prepared solely for internal use of Seres and Houlihan Lokey, and are subjective in many respects.

Although the Projections are presented with numerical specificity, they reflect numerous assumptions and estimates as to future events that our management believed were reasonable at the time the Projections were prepared, taking into account the relevant information available to Seres management at the time. However, this information is not fact and should not be relied upon as being necessarily indicative of actual future results. Important factors that may affect actual results and cause the Projections not to be achieved include general economic conditions, the commercial success of VOWST, competitive pressures, collaboration efforts, market acceptance by physicians, patients, hospitals, third-party payors and others in the medical community, reliance on third party manufacturers and other matters specific to the VOWST Business. The Projections are forward-looking statements and should be read in conjunction with the section of this proxy statement entitled “Cautionary Statement Regarding Forward-Looking Statements.” In addition, the Projections do not take into account any circumstances or events occurring after the date that they were prepared. As a result, there can be no assurance that the Projections will be realized, and actual results may be materially better or worse than those contemplated in the Projections. The inclusion of this information should not be regarded as an indication that the Seres Board, Seres, Houlihan Lokey or any other recipient of these Projections considered, or now considers, that actual future results will necessarily reflect the Projections. The Projections are not included in this proxy statement in order to induce any Seres stockholder to vote in favor of the Transaction Proposal or to influence any Seres stockholder to make any investment decision with respect to the Transaction.

The Projections should be evaluated, if at all, in conjunction with the financial statements of Seres, risk factors and other information regarding Seres and the VOWST Business contained in our public filings with the SEC. See “Where You Can Find More Information; Incorporation by Reference.”

Except to the extent required by applicable federal securities laws, we do not intend, and expressly disclaim any responsibility, to update or otherwise revise the Projections to reflect circumstances existing after the date the Projections were prepared or to reflect the occurrence of future events or changes in general economic or industry conditions, even in the event that any of the assumptions underlying any of the Projections are shown to be in error.

In light of the foregoing factors and the uncertainties inherent in the Projections, Seres stockholders are cautioned not to unduly rely on any of the Projections included in this proxy statement. For information on factors that may cause Seres’ future results to materially vary, see “Cautionary Statement Regarding Forward-Looking Statements.”

In considering the recommendation of the Seres Board to vote “FOR” the Transaction Proposal, you should be aware that, aside from their interests as Seres stockholders, our directors and executive officers have interests in the Transaction that are different from, or in addition to, the interests of our stockholders generally. These interests may present such directors and executive officers with actual or potential conflicts of interest, and these interests, to the extent material, are described below.

The Seres Board was aware of and considered these potential conflicts of interest, among other matters, in reaching its decision to approve the Transaction Proposal and the Transaction and to recommend that stockholders approve the Transaction Proposal as contemplated in this proxy statement.

After the Transaction, it is expected that all of the directors and executive officers of Seres will continue to provide services as directors and executive officers, respectively, of Seres. Seres will continue to provide indemnification and insurance coverage to the directors and executive officers of Seres.

The table below sets forth information regarding the options to purchase shares of Seres common stock and Seres restricted stock units (“RSUs”) held as of August 5, 2024 by each person who is or has been during the period beginning on January 1, 2023 through the date of this proxy statement, an executive officer or non-employee director of Seres. All outstanding equity awards issued to Seres’ non-employee directors under the terms of Seres’ non-employee director compensation program will automatically vest in full upon consummation of the Transaction. As described in more detail under “Employment Agreements” below, equity awards held by Seres executive officers may vest in the event of certain qualifying terminations of employment.

We have entered into employment agreements with each of our executive officers that provide for certain compensation and benefits in the event Seres terminates the executive officer’s employment without cause or the

executive officer resigns for good reason (in each case, a “Qualifying Termination”). For purposes of these agreements, Closing of the Transaction will constitute a change in control of Seres.

Under the terms of our employment agreement with Eric D. Shaff, the Company’s President and Chief Executive Officer, if Mr. Shaff experiences a Qualifying Termination, he will be entitled to receive 18 months of continued base salary, up to 18 months of continued medical, dental or vision coverage pursuant to COBRA, if elected, and immediate vesting of any time-based equity awards that would have otherwise become vested solely as a result of Mr. Shaff’s continued service during the twelve month period following his termination of employment. In the event such Qualifying Termination occurs within 60 days prior or 12 months following a change in control (in each case, the “CIC Period”), in lieu of the benefits described in the previous sentence, Mr. Shaff will be entitled to accelerated vesting of his time-based equity awards, 18 months of continued base salary, up to 18 months of continued medical, dental or vision coverage pursuant to COBRA, if elected, and a lump sum cash amount equal to 1.5 times his target bonus for the year of termination.

Under the terms of our employment agreement with each of our executive officers other than Mr. Shaff, if the executive officer experiences a Qualifying Termination, the executive officer will be entitled to receive 12 months of continued base salary and up to 12 months of continued medical, dental or vision coverage pursuant to COBRA, if elected. In the event such Qualifying Termination occurs within the CIC Period, in lieu of the benefits described in the previous sentence, the executive officer will be entitled to accelerated vesting of the executive’s time-based equity awards, 12 months of continued base salary, up to 12 months of continued medical, dental or vision coverage pursuant to COBRA, if elected, and a lump sum cash amount equal to 1.0 times the executive’s target bonus for the year of termination.

Each of the employment agreements contains a parachute payment “best pay” provision, under which payments and benefits in connection with a change in control made pursuant to the employment agreement or otherwise will either be made to the executive officer in full or as to such lesser amount as which would result in no portion of the payments and benefits being subject to an excise tax under Section 4999 of the U.S. Internal Revenue Code of 1986, as amended (the “Code”), whichever of the foregoing amounts is greater on an after-tax basis. Refer to the “—Golden Parachute Compensation” section below for quantification of the amounts that could become payable to our named executive officers under their employment agreements with us.

As of the date of this proxy statement, there are no new employment, equity or other arrangements or understandings between any executive officer or non-employee director of the Company, on the one hand, and SPN on the other hand, and no such arrangements or understandings are expected to be implemented.

The information set forth in the tables below is intended to comply with Item 402(t) of Regulation S-K, which requires disclosure of information about certain compensation for each of Seres’ named executive officers (“NEOs”) that is based on or otherwise relates to the Transaction. For purposes of Seres’ employment agreements with our NEOs, Closing of the Transaction will constitute a change in control of Seres.

The amounts indicated below are estimates based on multiple assumptions that may or may not actually occur or be accurate on the relevant date, including assumptions described below, and do not reflect certain compensation actions that may occur before the consummation of the Transaction. For purposes of calculating such amounts, on a pre-tax basis, Seres has assumed:

HSR Act. Under the HSR Act and the rules promulgated thereunder by the FTC, the Transaction cannot be completed until Seres and SPN each file a notification and report form with the FTC and the Antitrust Division of the DOJ under the HSR Act and the applicable waiting period thereunder has expired or been terminated.

At any time before or after consummation of the Transaction, notwithstanding the expiration or termination of the waiting period under the HSR Act, the FTC or the DOJ could take such action under the antitrust laws as it deems necessary or desirable in the public interest, including seeking to enjoin the completion of the Transaction, seeking divestiture of substantial assets of the parties or requiring the parties to license, or hold separate, assets or terminate existing relationships and contractual rights. At any time before or after the completion of the Transaction, and notwithstanding the expiration or termination of the waiting period under the HSR Act, any state could take such action under the antitrust laws as it deems necessary or desirable in the public interest. Such action could include seeking to enjoin the completion of the Transaction or seeking divestiture of substantial assets of the parties. Private parties may also seek to take legal action under the antitrust laws under certain circumstances.

SPN and Seres submitted the requisite notification and report forms under the HSR Act on June 24, 2024. The waiting period under the HSR Act expired on Wednesday, July 29 at 11:59 p.m., Eastern Time.

Under generally accepted accounting principles, upon completion of the Transaction, we will remove the net assets and liabilities related to the VOWST Business from our consolidated balance sheet. The results of operations of the VOWST Business will be treated as discontinued operations.

The following discussion is a summary of the material anticipated U.S. federal income tax consequences of the Transaction, but does not purport to be a complete analysis of all potential tax effects. The effects of other U.S. federal tax laws, such as estate and gift tax laws, and any applicable state, local, or non-U.S. tax laws are not discussed. This discussion is based on the Code, Treasury Regulations promulgated thereunder, judicial decisions, and published rulings and administrative pronouncements of the IRS, in each case in effect as of the date hereof. These authorities may change or be subject to differing interpretations. Any such change or differing interpretation may be applied retroactively in a manner that could adversely affect us. We have not sought and will not seek any rulings from the IRS regarding the matters discussed below. There can be no assurance the IRS or a court will not take a contrary position to that discussed below regarding the tax consequences of the Transaction.

The Transaction is a corporate action. Our U.S. stockholders will not recognize any gain or loss for U.S. federal income tax purposes directly as a result of the Transaction.

The Transaction will generally be treated as a sale of our assets in exchange for cash, certain contingent consideration and the assumption of certain liabilities. We expect to recognize gain on the sale of certain assets and loss on the sale of certain other assets, depending on the amount of consideration allocated to each asset compared with our tax basis in such asset. To the extent we recognize gain, we anticipate that our tax losses and other tax attributes will be available to offset all or a portion of our U.S. federal income tax liability resulting from such gain.

The determination of the amount of gain or loss recognized as a result of the Transaction and whether and to what extent our tax attributes will be available to offset the gain is highly complex and is based in part on facts that will not be known until the completion of the Transaction. While we are still assessing the impacts, it is possible that we will incur U.S. federal income tax as a result of the Transaction. In addition, to the extent our tax attributes are used to offset any gain, those tax attributes would not be available to offset other income or gain we recognize in the future, potentially increasing our future tax liabilities.

Concurrently with the execution of the Purchase Agreement, Seres, SPN and Bacthera AG entered into an Assignment and Termination of Manufacturing Agreement (the “Termination of Bacthera Manufacturing Agreement”), pursuant to which the parties agreed that concurrently with the Closing, Seres will assign that certain Long Term Manufacturing Agreement, dated November 8, 2021, as amended by that certain Amendment to the Long Term Manufacturing Agreement, dated December 14, 2022 (the “Bacthera Agreement”) between Seres and Bacthera AG, and, immediately thereafter, the Bacthera Agreement will be terminated by mutual agreement, upon the terms and subject to the conditions set forth therein. Pursuant to the Termination of Bacthera Manufacturing Agreement, concurrently with the Closing, SPN will pay a specified amount to Bacthera AG in full and final settlement of all outstanding liabilities owed to Bacthera AG pursuant to the Bacthera Agreement. At Closing, in exchange for a payment to be made by SPN to Bacthera AG, each of Bacthera AG and Seres will release one another from any losses, liabilities or other obligations arising thereunder with respect to the period ending as of the date of the Closing, including without limitation any milestone payments required to be paid to Bacthera AG thereunder. The Bacthera Agreement governed the general terms under which Bacthera AG agreed to (i) construct a dedicated full-scale production suite for Seres at Bacthera AG’s Microbiome Center of Excellence in Visp, Switzerland; and (ii) provide manufacturing services to Seres for VOWST.

If the Transaction is completed, we will no longer operate the VOWST Business. Following Closing, we expect to focus on advancing SER-155 and our other wholly-owned cultivated live biotherapeutic candidates for medically vulnerable patient populations with potential to address large commercial opportunities.

We are obligated to use the proceeds from the completion of the Transaction to fully repay our indebtedness under the Oaktree Credit Agreement, and we intend to use the remaining proceeds to support the further advancement of SER-155 and our other cultivated live biotherapeutic candidates and to fund its post-Closing obligations to pay 50% of the Net Loss, if any, the MSK Costs, the Safety Study Expenses and 80.1% of the Waltham Lease during the Profit Sharing Period as more fully described elsewhere in this proxy statement. Based on Seres’ current cash, our future operating plans, and the capital expected to be obtained from the Transaction

(accounting for estimated on-going costs related to the Transaction), we anticipate being able to extend our cash runway into the fourth quarter of 2025, subject to our material compliance with the Transition Services Agreement (and related receipt of the Installment Payments). Notwithstanding this present expectation, the Seres Board may use the proceeds of the Transaction for other purposes for the benefit of Seres and its stockholders, and in connection therewith may find it necessary or advisable to use portions of the proceeds from the Transaction for different or presently non-contemplated purposes.

The Transaction will not alter the rights, privileges or nature of the Seres common stock. A stockholder who owns shares of our common stock immediately prior to the completion of the Transaction will continue to hold the same number of shares immediately following the completion of the Transaction. Following Closing, Seres common stock will continue to be listed on Nasdaq Global Select Market under the ticker symbol “MCRB.”

The following is a summary of the material terms and conditions of the Purchase Agreement. This summary does not purport to be complete and may not contain all of the information about the Purchase Agreement that is important to you. This summary is qualified in its entirety by reference to the complete text of the Purchase Agreement, a copy of which is attached to this proxy statement as Annex A. We encourage you to read the Purchase Agreement carefully and in its entirety because it is the legal document that governs the Transaction.

Upon the terms and subject to the conditions of the Purchase Agreement, Seres is required to, and will cause its affiliates to, sell, convey, assign, transfer and deliver to SPN or its designated affiliates all of its and its affiliates’ rights, title and interest in and to the following (the “Acquired Assets”):

Upon the terms and subject to the conditions of the Purchase Agreement, the following assets (the “Excluded Assets”) will not be transferred to SPN and will be retained by Seres following Closing:

Upon the terms and subject to the conditions of the Purchase Agreement, at the completion of the Transaction, SPN and its affiliates are required to assume, and agree to pay or otherwise perform or discharge when due all of the liabilities of Seres and its affiliates listed below (the “Assumed Liabilities”):

Upon the terms and subject to the conditions of the Purchase Agreement, Seres and its affiliates will retain and be responsible for, and SPN and its affiliates will not assume, the following liabilities of Seres and its affiliates (the “Excluded Liabilities”):

As consideration for the Transaction, SPN has agreed to pay to Seres consideration as described below.

On the Closing date, SPN will pay Seres (i) a cash payment of $100 million, less approximately $17.9 million owed by Seres to an affiliate of SPN as of March 31, 2024 under the existing license agreement between Seres and the SPN affiliate, less approximately CHF2.0 million in satisfaction of fees due under the Bacthera Agreement, and (ii) a prepaid milestone payment of $60 million (the “Prepaid Milestone”) which is tied to the achievement of worldwide annual net sales of the Product of $150 million (the “First Sales Milestone”). The Prepaid Milestone will accrue interest at a rate of 10% per annum from the Closing date until the First Sales Milestone is achieved and, thereafter at 5% per annum until the earlier of (A) the date on which the Prepaid Milestone, plus accrued interest thereon, has been repaid in full by set-off and (B) the last day of the ten year Milestone Period. If any amount of the Prepaid Milestone (and any accrued interest thereon) remains outstanding as of following the last day of the Milestone Period, the balance thereof (together with any interest accrued thereon) will be forgiven and the right of set-off of SPN with respect thereto will be deemed forfeited by SPN.

Following Closing, SPN will pay to Seres the Installment Payments in the amounts specified below in cash on the dates specified below, provided that, as of the applicable payment date, Seres is in compliance with its obligations under the Transition Services Agreement in all material respects, as defined in the terms and conditions thereto:

The Installment Payment due on July 1, 2025 will be reduced by an amount related to certain employment obligations assumed by SPN through the period prior to the Closing date.

During the period from the Closing date until December 31 of the calendar year in which the tenth anniversary of the Closing date occurs (the “Milestone Period”), SPN will pay to Seres each of the following one-time contingent Milestone Payments (each corresponding milestone event, a “Milestone”) set out below following the first time that the Net Sales (as defined in the Purchase Agreement) of Product in the entire world reach the following thresholds, in accordance with the Purchase Agreement, provided that the Milestone Payment payable on achievement of the First Sales Milestone set out below will be funded at Closing as part of SPN’s obligation to pay Seres the Prepaid Milestone as noted above:

The Milestone Payments will be satisfied in the following manner: (i) first, by set-off against all accrued interest on the Prepaid Milestone until the amount of such accrued interest has been repaid in full, (ii) second, by set-off against the outstanding balance of the Prepaid Milestone until the Prepaid Milestone has been repaid in full, and (iii) thereafter, any amount due in respect of the Milestone Payments shall be paid in cash within 30 days following Seres’ delivery of an invoice. In the event that the First Sales Milestone is not achieved during the Milestone Period, SPN will not be entitled to a refund thereof. Instead, the right to repayment of the Prepaid Milestone will be forfeited by SPN. During the Milestone Period, SPN shall report to Seres within ten business days after the end of each calendar quarter the Net Sales of Product, determined in accordance with the International Financial Reporting Standards (“IFRS”).

During the Profit Sharing Period, Seres will be entitled to receive 50% of all Net Profit (as defined below) and will bear 50% of all Net Loss (as defined below), and Nestlé Health Science will be entitled to receive 50% of all Net Profit and will bear 50% of all Net Loss, as applicable.

“Net Profit” means a positive Net Profit/Net Loss, and “Net Loss” means a negative Net Profit/Net Loss.

“Net Profit/Net Loss” means, for any period, net sales of VOWST in the United States and Canada, plus any other income received from a third party that is attributable to VOWST in the United States or Canada or in connection with the grant of a license or sublicense with respect to VOWST in the United States and Canada as described in the Purchase Agreement, less allowable expenses directly attributable or reasonably allocable to certain development activities, commercialization activities, medical affairs activities, manufacturing activities or other relevant activities, as described in the Purchase Agreement, during such period.

SPN will provide an initial budget setting forth the projected Net Profit/Net Loss with respect to the Product, as further described in the Purchase Agreement, as promptly as practicable but in no event later than Closing, for the period from the Closing date through December 31, 2024. SPN will provide Seres with a good faith estimated budget prior to October 31, 2024, for the calendar year ending December 31, 2025. Such budgets are a non-binding estimated forecast for such period.

If SPN reasonably expects that the aggregate Net Loss or Ongoing Safety Study Expenses for such calendar quarter will exceed 115% of the estimated aggregate Net Loss (if applicable) or the Ongoing Safety Study Expenses, as applicable, as set forth in the budget for such calendar quarter, then SPN shall provide prompt notice thereof to Seres; provided, that the failure of SPN to provide such notice shall not relieve Seres of its obligations.

SPN will have the right to offset any Net Loss amounts owed to it by Seres against the Installment Payments or Milestone Payments in the event that Seres fails to timely make any payment of its share of a Net Loss that becomes due and payable under the Purchase Agreement; provided, that, Seres may elect to have any Net Loss amounts owed to SPN by Seres pursuant to the Purchase Agreement offset against amounts due and payable to Seres by SPN under the Transition Services Agreement.

During the Profit Sharing Period, Seres will reimburse Nestlé Health Science for the MSK Costs and the Ongoing Safety Study Expenses within 30 days following SPN’s delivery of an invoice therefor. Following the Profit Sharing Period, the Ongoing Safety Study Expenses will be borne exclusively by Nestlé Health Science.

The sale, conveyance, assignment, transfer and delivery of the Acquired Assets and the assumption by SPN of the Assumed Liabilities contemplated by the Purchase Agreement will take place on the second business day following such date that the last of the conditions to Closing have been satisfied or waived (other than those conditions that by their nature are to be satisfied by actions taken at Closing, but subject to the satisfaction or waiver of such conditions), or at such other time and place as SPN and Seres mutually agree in writing; provided, that in the event that the conditions to Closing are satisfied or waived (other than those conditions that by their nature are to be satisfied by actions taken at Closing, but subject to the satisfaction or waiver of such conditions) on or after the date that is three business days prior to the end of the month in which the last of such conditions has been satisfied, unless Seres and SPN mutually agree otherwise, Closing shall take place on the last business day of such month.

Seres’ representations and warranties to SPN in the Purchase Agreement relate to, among other things:

SPN’s representations and warranties to Seres in the Purchase Agreement relate to, among other things:

Many of the representations and warranties in the Purchase Agreement made by Seres and SPN are qualified by a “Material Adverse Effect” standard for purposes of determining whether the relevant condition to Closing, described in greater detail under “—Conditions to the Completion of the Transaction”, is satisfied (that is, they will not be deemed to be untrue or incorrect as of the Closing date, as if such representations and warranties were made as of the Closing date, unless their failure to be true or correct has had or would reasonably be expected to have a Material Adverse Effect).

For purposes of the Purchase Agreement, a “Material Adverse Effect” means any event, occurrence, effect, matter, change, development or state of facts that is materially adverse to (a) the Product, the Acquired Assets and the Assumed Liabilities, taken as a whole, or (b) Seres’ or its affiliate’s ability to consummate the Transactions; provided, however, that, in determining whether a Material Adverse Effect has occurred, there shall be excluded from the definition any event, occurrence, effect, matter, change, development or state of facts that results from: (i) changes or conditions affecting the industries in which the Product is exploited or the economy, in each case, in any territory in which the Product is exploited, (ii) any change in law or in GAAP or IFRS (in any territory in which the Product is exploited), or in the interpretation of any of the foregoing, (iii) conditions arising out of acts of terrorism, war conditions, natural disasters or other force majeure events, (iv) declining sales of the Product (including due to competition) or the failure to meet projections, forecasts, estimates or budgets with respect to the Product (any underlying cause for any such failure will not be excluded by this clause (iv)), (v) the announcement or pendency of the transactions contemplated by SPN or any action required to be taken by Seres or any of its affiliates pursuant to the terms of the Purchase Agreement or any action taken by Seres or any of its affiliates with SPN’s written consent, (vi) the failure to take any action that Seres or any of its affiliates have requested the consent of SPN to take and which SPN did not grant its consent with respect thereto, (vii) any action by Seres or its affiliates which SPN has expressly requested be taken or (viii) any acts or

omissions of SPN or any of its affiliates; except, in the cases of clauses (i), (ii), (iii) and (iv) only, to the extent Seres, the Product, the Acquired Assets or the Assumed Liabilities is disproportionately affected by such effect as compared to other similarly situated persons as Seres operating in the industries in which the Product is exploited.

Seres has agreed to certain covenants in the Purchase Agreement restricting the conduct of its business between the date of the Purchase Agreement and the completion of the Transaction (or any earlier termination of the Purchase Agreement).

As a general matter, between the date of the Purchase Agreement and the completion of the Transaction, Seres will, and will cause its affiliates to, (x) conduct its business with respect to the Product and the Acquired Assets in the ordinary course of business, and in all material respects in accordance with applicable law, (y) use its commercially reasonable efforts to preserve the goodwill of such business and the present relationships with employees (which efforts shall not include granting to employees special financial or equity incentives unless the parties mutually agree on a retention plan and funding responsibilities therefor), customers, vendors, suppliers, manufacturers and others having commercial relationships with such business and (z) except as the same may be restricted by applicable laws, consult with SPN regarding any material developments, strategic or other material decisions concerning the exploitation of the Product or the Acquired Assets.

Additionally, except as set forth on the Seller Disclosure Letter, Seres will not, and will cause its affiliates not to, without the prior written consent of SPN (not to be unreasonably withheld, conditioned or delayed), do any of the following:

As soon as possible following the date of the Purchase Agreement, Seres will call, give notice of, convene and hold a meeting of its stockholders to be held within 30 business days of the initial mailing of this proxy statement for the purpose of seeking stockholder approval of the Transaction. Unless the Seres Board has made a Change in Recommendation in accordance with the Purchase Agreement, Seres is required to include the Board Recommendation in this proxy statement, and will solicit, and use its reasonable best efforts to obtain, the approval of the Seres stockholders for the Transaction.

Subject to certain exceptions, Seres has agreed that it will not, and will cause its representatives not to, directly or indirectly:

Seres will, and Seres will instruct and use its reasonable best efforts to cause its representatives to, immediately cease and cause to be terminated any discussions, negotiations and communications with any person conducted prior to the date of the Purchase Agreement with respect to any Acquisition Proposal, or that would reasonably be expected to lead to an Acquisition Proposal, and will promptly terminate access by any such person to any physical or electronic data room hosted by Seres or its representatives relating to any such Acquisition Proposal and request the destruction or return (to the extent provided for by the applicable confidentiality agreement) of any and all nonpublic information previously provided to such person (other than SPN), in each case, as soon as reasonably practicable (but in any event within three business days) after the date of the Purchase Agreement.

Prior to the time, but not after, the stockholder approval for the Transaction is obtained, Seres may, in response to an unsolicited bona fide, written Acquisition Proposal from any person or group of persons, which Acquisition Proposal was made or renewed on or after the date of the Purchase Agreement and which did not result from a material breach of Seres’ non-solicitation obligations under the Purchase Agreement:

provided, Seres has provided prior written notice to SPN and the Seres Board determines in good faith after consultation with (A) Seres’ financial advisor and outside legal counsel that based on the information then available, that such Acquisition Proposal either constitutes a Superior Proposal or would reasonably be expected to result in a Superior Proposal and (B) Seres’ outside legal counsel, that the failure to take such action would reasonably be expected to be inconsistent with the fiduciary duties of the Seres Board to Seres’ stockholders under applicable law.

Seres is required to promptly (and, in any event, within twenty-four hours) notify SPN if (i) any written or other requests, inquiries, proposals or offers with respect to an Acquisition Proposal, or any inquiries, proposals, offers or requests for information relating to an Acquisition Proposal, are received by Seres or any of its representatives, (ii) any information is requested from Seres or any of its representatives in connection with any Acquisition Proposal or (iii) any discussions or negotiation with respect to an Acquisition Proposal are sought to be initiated or continued with Seres or any of its representatives, providing, in connection with such notice, unredacted copies of any written requests, inquiries, proposals or offers or other materials, including proposed agreements and a summary of the material terms and conditions of any such oral request, inquiry, proposal or offer (including any proposed term sheet, letter of intent, acquisition agreement or similar agreement with respect thereto), the name of such person or group and a summary of any material unwritten terms and conditions thereof, and thereafter shall keep SPN reasonably informed of the status and terms of any material developments, discussions or negotiations of such requests, inquiries proposals or offers (including by furnishing copies of any amendments or modifications thereto) on a prompt basis (and in any event within twenty-four hours of such material development, discussion or negotiation).

For the purposes of the Purchase Agreement, an “Acquisition Proposal” is any inquiry, proposal or offer from any person (other than SPN or any of its affiliates) concerning (x) a merger, consolidation, liquidation, recapitalization, share exchange or other business combination transaction involving Seres; (y) the issuance or acquisition of shares of capital stock or other equity securities of Seres in one or more related transactions which would cause any person which is not a stockholder of Seres on the date of the Purchase Agreement to own twenty percent or more of Seres’ outstanding equity, other than any issuance pursuant to the Securities Purchase Agreement; or (z) the sale, lease, exchange or other disposition of any significant portion of the Acquired Assets.

For purposes of the Purchase Agreement, a “Superior Proposal” is any unsolicited bona fide, written Acquisition Proposal (with percentages in the definition of Acquisition Proposal increased to fifty percent), which Acquisition Proposal was made or renewed on or after the date of the Purchase Agreement and did not arise out of a breach of Seres’ non-solicitation obligations under the Purchase Agreement on terms which the Seres Board determines in its good faith judgment, after consultation with Seres’ financial advisors and outside legal counsel, is reasonably expected to be consummated in accordance with its terms, taking into account all legal, financial, timing and regulatory aspects (including certainty of Closing) of the proposal and the person or group of persons making the proposal, and, if consummated, would result in a transaction more favorable to Seres’ stockholders (solely in their capacity as such), from a financial point of view, than the transactions contemplated by the Purchase Agreement (including after taking into account any revisions to the terms of the transactions contemplated by the Purchase Agreement pursuant to the Purchase Agreement and the time likely to be required to consummate such Acquisition Proposal).

Subject to specified exceptions described below, the Seres Board may not (i) effect a Change in Recommendation by withholding, withdrawing, qualifying or modifying (or publicly proposing or resolving to withhold, withdraw, qualify or modify), in a manner adverse to SPN, the Board Recommendation, failing to include the Board Recommendation in this proxy statement, failing to publicly reaffirm the Board Recommendation within three business days after SPN requests in writing that such action be taken, or adopting, approving, recommending or otherwise declaring advisable (or publicly proposing or resolving to adopt, approve, recommend or otherwise declare advisable) any Acquisition Proposal or making or authorizing the making of any public statement (oral or written) that has the substantive effect of such a withdrawal, qualification or modification or (ii) adopt, approve, recommend or declare advisable, or propose to approve, recommend or declare advisable, cause or permit Seres to execute or enter into an Alternative Acquisition Proposal in the form of any contract, including any letter of intent, memorandum of understanding, agreement in principle, acquisition agreement, merger agreement, option agreement, joint venture agreement, license agreement, partnership agreement, lease agreement or other agreement (other than an Acceptable Confidentiality Agreement) with respect to, or that is intended to or would reasonably be expected to lead to, any Acquisition Proposal or requiring, or reasonably expected to cause, Seres (or that would require Seres) to abandon, terminate, delay or fail to consummate, or that would otherwise materially impede, interfere with or be inconsistent with, the transactions contemplated by the Purchase Agreement.

Following (i) receipt of an unsolicited, bona fide written Acquisition Proposal by Seres that was made on or renewed on or after the date of the Purchase Agreement that did not result from a material breach of Seres’ non-solicitation obligations under the Purchase Agreement that has not been withdrawn and with respect to which Seres has received a written, definitive form of Alternative Acquisition Agreement, and the Seres Board determining in good faith, after consultation with its financial advisors and outside legal counsel, that such Acquisition Proposal constitutes a Superior Proposal, or (ii) the occurrence of an Intervening Event, the Seres Board may, at any time prior to the time the stockholder approval is obtained, make a Change in Recommendation with respect to such Superior Proposal, only if all of the following conditions are met:

Seres and SPN will use their reasonable best efforts to cause Closing to occur as promptly as practicable after the date of the Purchase Agreement, including taking all reasonable actions necessary (i) to comply promptly with all legal requirements that may be imposed on it or any of its affiliates with respect to Closing and (ii) to obtain or make each consent of or with a governmental entity that, if not obtained or made, would have a material adverse effect on the ability of the parties to consummate the Transaction; provided that SPN will not be required to license, sell, divest, hold separate, or otherwise dispose of any of SPN’s own assets or take any action that limits any freedom of action with respect to SPN’s ability to retain or operate any of its businesses, other than with respect to the Product.

As soon as reasonably practicable and advisable after the date of the Purchase Agreement, the parties will each make all required registrations and filings with governmental entities, and seek all required approvals under competition laws.

As of the date of this proxy statement, the parties have filed their respective notification and report form and the waiting period has expired pursuant to the HSR Act. The parties must use their respective commercially reasonable efforts to provide any additional information requested by any governmental entity under any applicable competition law as promptly as practicable and advisable.

Subject to applicable legal limitations, including redaction where necessary, and the instructions of any governmental entity, during the period prior to Closing, each party agrees, solely with respect to the transactions between the parties contemplated by the Purchase Agreement, to (i) cooperate and consult with the other party; (ii) furnish to the other party such necessary information and assistance as the other party may reasonably request in connection with its preparation of any notifications or filings with, or requests for additional information from, any governmental entity; (iii) keep each other apprised of the status of matters relating to the completion of the transactions contemplated by the Purchase Agreement, including promptly furnishing the other party with copies of notices or other communications received by such party from, or given by such party to, any third party and/or any governmental entity with respect to such transactions; (iv) permit the other party to review and incorporate the other party’s reasonable comments in any communication to be given by it to any governmental entity with respect to obtaining the necessary consents; and (v) not participate in any substantive meeting or discussion, either in person or by telephone, with any governmental entity unless, to the extent not prohibited by such governmental entity, it gives the other party the opportunity to attend and observe any such meeting or discussion.

SPN and Seres shall each be responsible for paying fifty percent of the fees payable (whether by SPN, Seres or their respective affiliates) to any governmental entity in connection with any filings made pursuant to competition laws in accordance with the Purchase Agreement.

Between the date of the Purchase Agreement and 11:59 p.m., Eastern Time, on the Employee Transfer Date (as defined in the Purchase Agreement), periodically upon SPN’s reasonable request, Seres agrees to update the list of employees dedicated to the manufacture and supply chain operations of the Product and any additional employees identified by the parties that would meet the business needs of SPN with respect to the ongoing business of the Product under its ownership (the “Employee List”) with any changes allowed for under the Purchase Agreement or the Employee Support Agreement. SPN may in its sole discretion offer employment to any employees listed (each such employee, an “Employee”) on the Employee List effective as of the Employee Transfer Date. SPN will extend any such employment offers to such employees and will provide Seres with copies of all such employment offers, in each case, at least five business days prior to Closing. Each Employee who is offered and accepts SPN’s offer of employment is referred to as a “Transferring Employee.” With respect to any Employee listed on the Employee List who is offered and accepts SPN’s offer of employment but who is absent on the Employee Transfer Date due to short-term or long-term disability leave or parental leave (collectively, the “Employees on Disability Leave”), any such Employee on Disability Leave must be able to commence active employment and present themselves to SPN or one of its affiliates for active employment within three months (or twenty weeks solely for purposes of parental leave) following the Employee Transfer Date or such Employee on Disability Leave’s offer will no longer be valid. Each Employee on Disability Leave who returns to work not later than three months (or twenty weeks solely for purposes of parental leave) following the Employee Transfer Date will become a Transferring Employee effective as of the date of such

return and will remain an employee of Seres (or one of its affiliates) until such date of their return. Each Employee (including any Employee on Disability Leave) shall remain an employee of Seres (or one of its Affiliates) and continue participating in any Seller Benefit Plan in which he or she participated immediately prior to the Employee Transfer Date (subject to its terms) until such Employee becomes a Transferring Employee of SPN (or one of its Affiliates). The offers of employment extended by SPN to Employees under the Purchase Agreement (the “Qualifying Offers”) will be on terms determined by SPN in its sole discretion, provided, however, that SPN agrees that, during the period commencing on the Closing date and ending on the first anniversary of the Closing date (or, if earlier, a relevant Transferring Employee’s termination date), each Transferring Employee will be provided with:

Notwithstanding the foregoing, each Qualifying Offer shall be subject to the satisfaction of SPN’s standard hiring requirements, each Employee’s confirmation in the Employee’s Qualifying Offer that the Employee acknowledges and agrees that the Employee does not have “Good Reason” under the Severance Plan (as defined below) on or prior to the hire date or as a result of any of the terms of such Qualifying Offer and each Employee’s confirmation in the Employee’s Qualifying Offer that, in the event the Employee accepts SPN’s offer of employment, the Employee consents and agrees to Seres providing SPN the Employee’s previously completed Form I-9 and supporting documentation verifying the Employee’s identity and authorization to work in the United States (and that Seres is an intended third party beneficiary of such consent and agreed). SPN’s (or an affiliate’s) refusal to hire any employee due to his or her failure to satisfy such standard hiring requirements, as determined by SPN (or an affiliate) in its sole discretion, will not constitute a failure by SPN (or an affiliate) to provide a Qualifying Offer to such employee, and nothing in the Purchase Agreement will prohibit SPN from amending or terminating any benefit plans, arrangements or agreements in accordance with their terms after the Employee Transfer Date or from terminating the employment of any Transferring Employee to the extent permitted by applicable laws. Seres will, subject to Seres’ prior receipt of an Employee’s executed Qualifying Offer or of SPN’s certification to Seres of such execution and no later than one day prior to Closing, provide SPN with copies (the originals of which may be retained by Seres) of such Transferring Employee’s previously completed Form I-9 and supporting documentation verifying their identity and authorization to work in the United States.

SPN expressly agrees as of Closing to honor the obligations and liabilities of Seres under the Seres Therapeutics, Inc. Change in Control Severance Plan (the “Severance Plan”) with respect to each Transferring Employee to the extent that any such obligation or liability is triggered under the Severance Plan during the one (1)-year period following the Closing date, but shall not expressly assume the Severance Plan.

SPN agrees that, from and after the Employee Transfer Date, SPN will use commercially reasonable efforts to grant all Transferring Employees credit for any employment service with or for the benefit of Seres or its affiliates earned prior to the Employee Transfer Date for purposes of vesting (other than for purposes of any annual retirement contribution) and eligibility under any employee benefit plan, program or arrangement that may be established or maintained by SPN (“Purchaser Benefit Plans”) and, for purposes of vacation and severance plans established or maintained by SPN, for purposes of benefit accrual. In addition, SPN must use commercially reasonable efforts to (i) waive all pre-existing condition exclusion and actively-at-work requirements and similar limitations, eligibility waiting periods and evidence of insurability requirements under any Purchaser Benefit Plans to the extent waived or satisfied by a Transferring Employee under any Seller Benefit Plan as of the

Employee Transfer Date , and (ii) cause any covered expenses incurred on or before the Employee Transfer Date by any Transferring Employee to be taken into account for purposes of satisfying applicable deductible, coinsurance and maximum out-of-pocket provisions after the Employee Transfer Date under any applicable Purchaser Benefit Plan. The parties acknowledge and agree that from and after the Employee Transfer Date , Seres and its affiliates shall retain all liabilities under all Seller Benefit Plans, except as otherwise described in the Purchase Agreement. Effective as of the Employee Transfer Date, the Transferring Employees will cease all active participation in and accrual of benefits under the Seller Benefit Plans.

Seres will, or will cause an affiliate to, offer and continue to provide, as applicable, continuation coverage pursuant to Section 4980B of the Code and Section 601 of the Employee Retirement Income Security Act of 1974, as amended (“ERISA”) to all M&A qualified beneficiaries (as defined in Treas. Reg. § Section 54.4980B-0, Q&A-4(a)) under the applicable Seller Benefit Plans.

Seres and its affiliates shall pay to the Transferring Employees all unused accrued vacation balances pursuant to Seres’ or its affiliates’ applicable policies and law, on or as soon as administratively practicable after the Employee Transfer Date , but in any case, no later than the date required by applicable law.

With respect to any situation in which Seres or its affiliates effectuate terminations or layoffs prior to the Employee Transfer Date, such that there is or is deemed to be an employment loss or layoff triggering notice requirements and/or liability under the Worker Adjustment and Retraining Notification Act, 29 U.S.C. § 2101 et seq. (the “WARN Act”),

Seres or its affiliates shall be responsible for all liabilities and obligations, including relating to providing any notices, arising under or pursuant to the WARN Act thereunder , subject to the terms of the Employee Support Agreement.

Subject to the terms of the Employee Support Agreement, Seres and its affiliates shall retain all liabilities with respect to the Transferring Employees under the commission, equity and equity-based, and other retention and bonus plans sponsored or maintained by Seres or any of its affiliates with respect to the period prior to the Employee Transfer Date. SPN will, or will cause one of its affiliate to, pay to the Transferring Employees annual cash bonuses for the calendar year in which the Closing occurs, subject to such terms and conditions as otherwise would be applicable to the payment thereof under Seres’ plan but assuming one hundred percent (100%) performance for the period prior to Closing, and subject to such conditions as otherwise would be applicable to the payment thereof under SPN’s plan from and after Closing, and payable at such time as such amounts would have been paid to the Transferring Employees under SPN’s plan (and in no event later than March 15 following the calendar year in which the Closing occurs) and further subject to Seres and its affiliates providing such information as is reasonably necessary or requested by SPN to calculate and make such payments provided that, for the avoidance of doubt, in no event shall such bonuses be eligible compensation under the qualified plans maintained by SPN and its affiliates. Following the Employee Transfer Date, Transferring Employees who are eligible to participate in annual incentive or short-term bonus and/or commission plans sponsored or maintained by SPN or its affiliates shall participate in such plans for the balance of the fiscal year in which the Employee Transfer Date occurs consistent with SPN’s Qualifying Offer obligations.

At least ten business days prior to Closing (based on the information then available to Seres) and promptly upon obtaining any additional or different information that would impact such calculations, Seres will determine whether any payments or benefits to any Transferring Employees as a result of or in connection with the Transaction will be deemed to constitute “parachute payments” (within the meaning of section 280G of the Code and the regulations promulgated thereunder), and, if applicable, provide a copy of such analysis for Transferring Employees to SPN and consider in good faith its reasonable comments thereon.

The consummation of the Transaction is not subject to any financing conditions (except the closing of the Equity Financing Transaction). SPN represents that it has sufficient funds to make the payments required under the Purchase Agreement, including the Closing Date Payment, and to perform the obligations to be performed as of and following Closing (including payment of the Closing Date Payment) and to pay the fees and expenses of SPN and its applicable affiliates incurred in connection with the transactions contemplated by the Purchase Agreement.

Subject to certain exceptions set forth in the Purchase Agreement, the Company has agreed that the Company will not, and will cause its affiliates not to, directly or indirectly:

Additionally, subject to certain exceptions set forth in the Purchase Agreement, during the Restrictive Period, the Company and SPN agreed that they will not, and will cause their affiliates not to, directly or indirectly, knowingly publish or communicate to any person any disparaging remarks, comments or statements concerning the other party or its affiliates in any way that would reasonably be understood to adversely affect the goodwill or impugn the reputation of any such entity. Notwithstanding the foregoing, nothing in the Purchase Agreement, will preclude either party from (A) providing truthful testimony obtained through court order, deposition, subpoena or similar legal process, (B) providing any truthful information pursuant to investigation by any governmental entity or (C) providing any truthful information pursuant to any claim by either party under the Purchase Agreement or any other agreement to which SPN or any of its affiliates, on the one hand, and Seres or any of its affiliates, on the other hand, are parties.

Further, subject to certain exceptions set forth in the Purchase Agreement, SPN has agreed that SPN will not, and will cause its affiliates not to, directly or indirectly, for the period beginning on the Closing date and ending on the first anniversary of the Closing date, hire or engage or solicit for employment or services any such employee who is not a Transferring Employee (a “Non-Transferring Employee”), or cause, induce or encourage any such Non-Transferring Employees to leave employment with Seres or its affiliates; provided, however, that SPN may solicit (or hire) any person (i) who contacts SPN or such Affiliate on his or her own initiative; (ii) who responds to a general solicitation of employment through an advertisement not specifically targeted at Seres, its affiliates or any of their respective officers or employees; or (iii) whose employment has been terminated by Seres or its affiliate at least six months prior to such solicitation.

The Purchase Agreement contains other covenants relating to confidentiality, access to information, publicity, accounts settlement, transfer of Acquired Regulatory Approvals, third party consents, governmental consents, support, regulatory matters, trade notification, intellectual property, further assurances and wrong pockets, tax matters, employee matters, bulk transfer laws, this proxy statement, the special meeting, stockholder litigation, restrictions on indebtedness, and the Ongoing Safety Study.

Each party’s obligation to complete the Transaction is subject to the satisfaction, or (to the extent permitted by law) waiver, of certain conditions, including:

The obligations of Seres to complete the Transaction are also subject to the satisfaction, or waiver, of the following conditions:

The obligations of SPN to complete the Transaction are also subject to the satisfaction, or waiver, of the following conditions:

The Purchase Agreement may be terminated at any time prior to the completion of the Transaction:

Seres has agreed to pay to SPN $4.7 million for the reimbursement of expenses in cash (the “Reimbursement Expense Amount”) in the following circumstances:

In no event will Seres be obligated to pay the Reimbursement Expense Amount on more than one occasion.

The representations and warranties made by the parties in the Purchase Agreement (other than certain fundamental and tax representations set forth in the Purchase Agreement) shall survive Closing until the first anniversary of the Closing date. Certain fundamental and tax representations will survive Closing until the date that is 30 days after the expiration of the applicable statute of limitations. The covenants and agreements to be performed by or on behalf of a party prior to Closing will terminate as of Closing, provided that, notwithstanding such termination, SPN shall be entitled to make a Claim in respect of a breach of the covenants and agreements regarding conduct prior to closing for a period of six months following Closing. The covenants and agreements that by their terms are to be performed by or on behalf of a party after Closing will survive until the date that such covenants and agreements are fully performed.

The termination of the representations, warranties, covenants and agreements provided under the Purchase Agreement will not affect the rights of a party in respect of any claim made by such party in a writing and received by Seres (in the case of a claim made by SPN) or SPN (in a case of a claim made by Seres) prior to the expiration of the applicable survival period.

From and after Closing, Seres is required to indemnify, save, defend and hold harmless SPN, its affiliates and each of their respective officers, directors, employees, agents and representatives (collectively, the “Purchaser Indemnified Parties”) for certain damages incurred by any such Purchaser Indemnified Party that arise out of or result from:

From and after Closing, SPN is required to indemnify, save, defend and hold harmless Seres, its affiliates and each of their respective officers, directors, employees, agents and representatives (the “Seller Indemnified Parties”) for certain damages incurred by any such Seller Indemnified Party that arise out of or result from:

Except as otherwise set forth in any Ancillary Agreement entered into in connection with the Purchase Agreement, whether or not the Transaction is consummated, each party shall bear its own expenses with respect to the transactions contemplated by the Purchase Agreement.

The Purchase Agreement may not be amended except upon the execution and delivery of a written agreement executed by both parties. Any term or condition of the Purchase Agreement may be waived at any time by the party that is entitled to the benefit thereof, but no failure or delay on the part of a party in exercising any right, power or remedy under the Purchase Agreement will operate as a waiver thereof; nor shall any single or partial exercise of any such right, power or remedy preclude any other or further exercise thereof or the exercise of any other right, power or remedy thereunder. No waiver of any provision of the Purchase Agreement will be effective unless the same shall be in writing and signed by the party giving such waiver.

The Purchase Agreement is governed by, and enforced in accordance with, the internal laws of the State of Delaware, without giving effect to any laws, rules or provisions of the State of Delaware that would cause the application of the laws rules or provisions of any jurisdiction other than the State of Delaware.

As a condition to Closing, the parties will enter into the Transition Services Agreement, in substantially the form set forth as Exhibit H to the Purchase Agreement. The Transition Services Agreement which will provide for services to be performed by Seres in order to facilitate a transition of the VOWST Business to SPN and its affiliates. The scope of the transition services is expected to include the provision of certain manufacturing services and certain administrative functions related to the VOWST Business and operations, including the maintenance of certain manufacturing services and the related facility in which such services are currently conducted. Seres will provide the manufacturing services until December 31, 2025, which period may be extended by up to six months (solely to ensure the manufacturing facility is in a state of compliance with the biologics license application for VOWST and readiness for potential regulatory inspection), and other services, until the later of the period specified in the schedule to the Transition Services Agreement for each service and June 30, 2026. SPN will agree to pay Seres for certain fixed costs, including a monthly fixed fee for preserved raw material suspension manufacturing, and will reimburse Seres for certain costs of the transition services performed by Seres under the Transition Services Agreement. The know-how and other intellectual property generated in connection with the performance of the Transition Services Agreement will be owned by SPN with Seres having a non-exclusive license to such know-how and other intellectual property under the Cross-License Agreement. During the term of the Transition Services Agreement, upon SPN’s request, Seres will transfer the manufacturing services to a third party service provider designated by SPN. In the event of a material failure by Seres to deliver preserved raw material suspension under the Transition Services Agreement, SPN will have step-in rights to negotiate to enter into a direct lease with the landlord of the manufacturing facility with respect to the portion of such facility used in connection with the VOWST Business or to cause such services to be performed, with any reasonable out-of-pocket costs and expenses incurred in connection therewith reimbursed by Seres.

As a condition to Closing, the parties will also enter into the Cross-License Agreement, in substantially the form set forth as Exhibit D to the Purchase Agreement. Under the Cross-License Agreement, Seres will grant to SPN a perpetual, worldwide, non-exclusive, fully paid-up license under certain Company patents that have been issued or will issue in the future and current know-how controlled by Seres that is not transferred to SPN pursuant to the Purchase Agreement. In the field of the treatment of CDI and rCDI and associated complications (collectively, the “CDI Field”) the license to SPN under such Company patents and know-how would be exclusive to SPN for five years after Closing and co-exclusive between SPN and Seres following that five year period. The license from Seres to SPN is to issued Seres patents that currently or in the future cover the Product or improvements thereof, and know-how that is used or reasonably useful in connection with the exploitation of the VOWST Business. Seres will also grant SPN an exclusive, perpetual, worldwide, fully paid-up license under issued Seres patents that currently or in the future cover the Product and improvements thereof and know-how that is used or reasonably useful in connection with the exploitation of the Product to exploit SER-262 in the CDI Field. SPN will grant to Seres a perpetual, worldwide, non-exclusive license under the patents and know-how that are transferred to SPN pursuant to the Purchase Agreement or developed under the Transition Services Agreement, for the Company’s products for use outside of the CDI Field, and after five years from Closing for Seres products containing designed, cultivated, bacterial consortia not manufactured using human stool (excluding SER-262) in the CDI Field. From and after Closing, certain license agreements between the Company, SPN, and/or their respective affiliates will terminate and be of no further force or effect, except as contemplated by the Purchase Agreement.

Concurrently with the execution of the Purchase Agreement, the directors, executive officers and certain stockholders affiliated with Flagship Pioneering, Inc. entered into the Support Agreements, in substantially the form set forth as Exhibits A-1 and A-2 to the Purchase Agreement and Annex C to this proxy statement, pursuant to which, among other things and subject to the terms and conditions therein, such parties have agreed, in their capacities as holders of the Subject Shares, to vote all Subject Shares beneficially owned by such parties at every meeting of the stockholders of Seres (including the special meeting) (i) in favor of adopting and approving the Purchase Agreement and the transactions contemplated by the Purchase Agreement, (ii) against any proposal that would otherwise be reasonably be expected to adversely affect the transactions contemplated by the Purchase

Agreement, (iii) against any Acquisition Proposal and (iv) in favor of approving any proposal to adjourn or postpone the special meeting to a later date, if there are not sufficient votes for the adoption of the Purchase Agreement on the date on which such meeting is held. In addition, each stockholder party to a Support Agreement provided an irrevocable proxy to SPN to vote such party’s Subject Shares in favor of adopting and approving the Purchase Agreement.

The Support Agreements for the directors and executive officers shall terminate automatically upon the earliest of (i) the termination of the Purchase Agreement in accordance with its terms, (ii) a Change in Recommendation, (iii) Closing of the Purchase Agreement, and (iv) the date on which the parties agree in writing to terminate each Support Agreement. The Support Agreements for the stockholders affiliated with Flagship Pioneering, Inc. shall terminate automatically upon the earliest of (i) the termination of the Purchase Agreement in accordance with its terms, (ii) Closing of the Purchase Agreement, and (iii) the date on which the parties agree in writing to terminate each Support Agreement.

As a condition to Closing, the parties will enter into the Securities Purchase Agreement, in substantially the form attached as Exhibit L to the Purchase Agreement and Annex D to this proxy statement, pursuant to which SPN will agree to purchase 14,285,715 Shares, at a purchase price per share of $1.05, for an aggregate purchase price of $15 million. Under the terms of the Securities Purchase Agreement, SPN will agree not to sell or transfer the Shares for a period of six months after Closing, subject to certain customary exceptions. Seres will agree to register the resale of the Shares by SPN within 90 days of Closing. In addition, under the terms of the Securities Purchase Agreement, for as long as SPN, together with its affiliates, beneficially owns at least 10% of Seres’ outstanding shares of common stock, Seres will agree to take such action within its control to include one individual designated by SPN in the slate of nominees recommended by the Seres Board (or the applicable committee of the Seres Board) to Seres’ stockholders for election to the Seres Board at the applicable stockholder meeting. The Securities Purchase Agreement will contain customary representations and warranties and closing conditions.

As a condition to Closing, the parties will also enter into Assignment and Assumption of Lease Agreements, in substantially the form set forth as Exhibit C to the Purchase Agreement (the “Assignment and Assumption Agreements”). Under the Assignment and Assumption Agreements, Seres will assign to SPN or its designated affiliates Seres’ rights in, to and under certain real property leases, and SPN or its designated affiliates will assume the liabilities related thereto. During the Profit Sharing Period, Seres will retain certain ongoing obligations with respect to liabilities due and payable to the landlord under the Waltham Lease, including reimbursing SPN for 80.1% of all rent and other costs due to the landlord under the Waltham Lease.

As a condition to Closing, the parties will also enter into the Employee Support Agreement, in substantially the form set forth as Exhibit K to the Purchase Agreement. Under the Employee Support Agreement, among other things and subject to the terms and conditions therein, certain Seres employees related to the VOWST Business who accept employment with SPN will provide the services they provided to Seres prior to the Transaction to SPN, as well as other services as SPN may reasonably request, from Closing until the day prior to the beginning of SPN’s next pay period following the Closing. SPN will reimburse Seres’ out of pocket costs in connection with such employees’ services, including certain compensation and benefits paid or provided to such employees, in each case pursuant to the terms of the Employee Support Agreement.

The audited historical financial statements of Seres and its subsidiaries for the years ended December 31, 2023 and 2022 are contained in Seres’ Current Report on Form 8-K filed on August 15, 2024 that is incorporated by reference into this proxy statement. The unaudited historical financial statements of Seres and its subsidiaries as of and for the three and six months ended June 30, 2024 are contained in Seres’ Quarterly Report on Form 10-Q for the quarter ended June 30, 2024, and are incorporated by reference into this proxy statement.

See the section of this proxy statement entitled “Unaudited Combined Financial Statements of the VOWST Business” beginning on page F-2 for the unaudited financial statements of the VOWST Business for the years ended December 31, 2023 and 2022, and the unaudited interim financial statements of VOWST Business for the six months ended June 30, 2024 and 2023.

On August 5, 2024, Seres Therapeutics, Inc. (“Seres” or the “Company”) and Société des Produits Nestlé S.A., (“SPN”), entered into an Asset Purchase Agreement (the “Purchase Agreement”) pursuant to which Seres agreed to sell Seres’ VOWST microbiome therapeutic business (the “VOWST Business”), including inventory and equipment, certain patents and patent applications, know-how, trade secrets, trademarks, domain names, marketing authorizations and related rights, documents, materials, business records and data and contracts that are used or held for use primarily in the development, commercialization and manufacturing of the microbiome product sold under the brand name VOWST, formerly known as SER-109 (the “Product”) to SPN and its designated affiliates (collectively, “Nestlé Health Science”), and Nestlé Health Science will assume certain liabilities from Seres (the “Transaction”). As per the Purchase Agreement, the Transaction will close when certain conditions, including Seres’ shareholder approval are met (“Closing”).

In addition to the tangible and intangible assets sold, the Company will also transfer to Nestlé Health Science (i) the license agreement with Memorial Sloan Kettering Cancer Center (the “MSK Agreement”), (ii) the supply agreement with Genlbet, and (iii) the contract manufacturing agreement with Bacthera (the “Bacthera Agreement”). In addition, the Company agreed to provide certain services to Nestlé Health Science following the date of Closing pursuant to a Transition Services Agreement (the “Transition Services Agreement”). In connection with the Transition Services Agreement, the Company will provide manufacturing services until December 31, 2025, and other services until the later of the period specified in the schedule to the Transition Services Agreement for each service or June 30, 2026. The Company also agreed to assign certain lease agreements at donor collection facilities located in Tempe, Arizona and Irvine, California, as well as the Company’s donor screening laboratory in Pennsylvania and the Company’s lease of laboratory and office space used for quality release testing located in Waltham, Massachusetts (“Waltham Lease”). Further, during the period from the date of Closing until December 31, 2025, the Company will be entitled to receive 50% of all net profits of the VOWST Business in the United States and Canada and will bear 50% of all net loss of the VOWST Business in the United States and Canada, as applicable (the “Profit Sharing Payments”).

As a condition to Closing, Seres and SPN will enter into a Securities Purchase Agreement (“Securities Purchase Agreement”), in which SPN will agree to purchase 14,285,715 shares of the Company’s common stock, par value $0.001 per share (the “Seres common stock”) at Closing at a purchase price per share of $1.05, resulting in aggregate proceeds of $15.0 million to the Company concurrently with the closing of the Transaction.

The following unaudited pro forma combined financial information is based on Seres’ historical consolidated financial statements and are presented to illustrate:

The unaudited pro forma combined statements of operations of Seres reflect Seres’ results of operations as if the Transaction had occurred on January 1, 2023. The unaudited pro forma combined balance sheet of Seres reflects

the financial position as if the Transaction had occurred on June 30, 2024. Subject to stockholder approval and in the period when that occurs, which is expected to be the third quarter of 2024, the VOWST Business’s historical financial results for periods prior to the Transaction will be reflected in Seres’ consolidated financial statements as discontinued operations.

The unaudited pro forma combined financial information and the accompanying notes should be read in conjunction with:

The unaudited pro forma combined financial information has been prepared in accordance with Article 11 of Regulation S-X as amended by the final rule, Release No. 33-10786 “Amendments to Financial Disclosures about Acquired and Disposed Businesses”. Article 11 of Regulation S-X requires that pro forma financial information include the following pro forma adjustments to the historical financial of the registrant as follows:

In addition, Regulation S-X permits registrants to reflect adjustments that depict synergies and dis-synergies of the acquisitions and dispositions for which pro forma effect is being given in our disclosures as management adjustments. We have determined not to disclose such adjustments because we do not believe presenting such adjustments would enhance an understanding of the pro forma effects of the Transaction.

There are no autonomous entity adjustments included in the pro forma financial information.

The transaction accounting adjustments to reflect the sale of the VOWST Business in the unaudited pro forma combined financial information include:

The effects of recording certain adjustments associated with contingent consideration related to i) future fixed installment payments to be received by the Company after it performs services and is determined by SPN to be in material compliance with the terms and conditions of the Transition Services Agreement and ii) certain milestone payments received by the Company after the Product has achieved net sales-based milestones, have been excluded as these amounts have been accounted for as gain contingencies in accordance with ASC 450, Contingencies. These contingent receivables will be recognized in earnings after the contingencies are resolved. Additionally, the Company has estimated costs associated with certain accrued liabilities due to SPN as a loss contingency in accordance with ASC 450, Contingencies. This contingent liability has been accrued on the Company’s pro forma combined balance sheet. The unaudited pro forma combined financial information does not reflect transaction accounting adjustments for the Transition Services Agreement entered into in connection with the Transaction. Pro forma adjustments have not been made related to the Transition Services Agreement as the services cannot be reasonably estimated at this time.

The estimated pre-tax gain of $143.5 million on the sale of the VOWST Business has been calculated as follows:

The estimated pre-tax gain of $143.5 million has been excluded from the pro forma combined statement of operations as this amount pertains to discontinued operations and does not impact income from continuing operations.

The unaudited pro forma combined financial information is presented for informational purposes only and is based upon estimates by Seres’ management, which are based upon available information and certain assumptions that Seres’ management believes are reasonable as of the date of this filing. The unaudited pro forma combined financial information is not intended to be indicative of the actual financial position or results of operations that would have been achieved had the Transaction been consummated as of the periods indicated above, nor does it purport to indicate results which may be attained in the future. Actual amounts could differ materially from these estimates.

The unaudited pro forma combined balance sheet as of June 30, 2024 and the unaudited pro forma combined statement of operations for the six months ended June 30, 2024 and years ended December 31, 2023 and 2022 should be read in conjunction with the notes thereto.