Seres Therapeutics, Inc.

Nature of the Business and Basis of Presentation

Seres Therapeutics, Inc. (the “Company”) was incorporated under the laws of the State of Delaware in October 2010 under the name Newco LS21, Inc. In October 2011, the Company changed its name to Seres Health, Inc., and in May 2015, the Company changed its name to Seres Therapeutics, Inc. The Company is a clinical-stage company focused on improving patient outcomes in medically vulnerable populations through discovery and development of novel live biotherapeutics. The Company led the successful development and approval of VOWST (previously referred to as SER-109), the first FDA-approved orally administered microbiome therapeutic and a Breakthrough Therapy designated drug, which was sold to Nestlé Health Science (as defined below) in September 2024. The Company's live biotherapeutic product (“LBP”) candidates, including SER-155, SER-603, SER-147, and other potential candidates in earlier development, are consortia of bacteria designed to optimize specific, targeted pharmacological properties, and are formulated for oral delivery. The Company is designing LBP candidates to target the prevention and treatment of a broad swath of infections, and to treat inflammatory and immune (“I&I”) diseases by modulating host function to increase epithelium integrity and to induce immune homeostasis and tolerance, as well as to prevent the colonization and overgrowth of pathogens in the gastrointestinal (“GI”) tract.

SER-155, the Company's most advanced LBP candidate, is an investigational, oral, live biotherapeutic designed to decolonize GI pathogens, improve GI epithelial barrier integrity, and induce immune homeostasis to prevent bacterial bloodstream infections (“BSIs”), including those that can harbor antimicrobial resistance (“AMR”), as well as other pathogen-associated negative clinical outcomes in patients undergoing allogeneic hematopoietic stem cell transplantation (“allo-HSCT”). In the Company's placebo-controlled Phase 1b study of SER-155 in allo-HSCT, SER-155 was associated with a 77% relative risk reduction in bacterial BSIs and a significant reduction in systemic antibiotic exposure as well as a lower incidence of febrile neutropenia, as compared to placebo through day 100 post HSCT. SER-155 was generally well tolerated, with no observed treatment-related serious adverse events. Following advancement of key startup activities for the SER-155 Phase 2 study in allo-HSCT, including the submission of a final protocol to the FDA in January 2026, study site evaluation and qualification with its CRO, and manufacturing of drug substance, the Company has paused additional investment in that program while continuing to seek funding for the Phase 2 study.

The clinical data from the SER-155 Phase 1b study in allo-HSCT, along with the Company's extensive preclinical and translational clinical data compiled over the past decade support and inform the advancement of the Company's earlier stage programs targeting I&I diseases. The Company is evaluating SER-155 in immune checkpoint-related enterocolitis, or irEC, and the Company is developing SER-603, broadly in inflammatory bowel disease, or IBD, including ulcerative colitis, or UC, and Crohn's disease. The Company is currently exploring potential collaborations related to those I&I disease programs.

The Company has built and deploys a reverse translational platform and knowledge base for the discovery and development of live biotherapeutics, and maintains extensive proprietary know-how that may be used to support future research and development efforts. This platform incorporates high-resolution analysis of human clinical data to identify microbiome biomarkers associated with disease and non-disease states; preclinical screening using human cell-based assays and in vitro/ex vivo and in vivo disease models customized for live biotherapeutics; and a strain library and associated microbiological capabilities that spans broad biological and functional breadth. This platform and knowledge base are integrated through a proprietary knowledge graph and agentic artificial intelligence, enabling rapid identification of specific microbes, microbial genes, and microbial metabolites/peptides associated with disease and the design of therapeutic consortia of bacteria for specific pharmacological properties to restructure the gut microbiome and modulate functional pathways associated with disease. In addition, the Company owns a valuable intellectual property estate related to the development and manufacture of live biotherapeutics.

At a special meeting of stockholders held on September 26, 2024, the Company’s stockholders approved, and on September 30, 2024(the "Closing Date"), the Company completed, the sale (the “Transaction”) of its 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 as provided for in accordance with the terms of the Purchase Agreement (the “Product”), to Société des Produits Nestlé S.A. (“SPN”), a wholly-owned subsidiary of Nestlé S.A., and its designated affiliates (collectively, “Nestlé Health Science”) pursuant to the Asset Purchase Agreement, dated as of August 5, 2024 (the “Purchase Agreement”), by and among the Company and SPN, and a wholly-owned subsidiary of Nestlé S.A. As consideration for the Transaction, SPN paid or agreed to pay, as applicable, the following Transaction Consideration:

(i)

a cash payment, which was paid upon completion of the Transaction (“Closing”), of $100,000, less approximately $17,857 owed by the Company to an affiliate of SPN as of March 31, 2024 under the prior license agreement between the Company and the SPN affiliate, less approximately CHF 2,000 in satisfaction of fees due under the Bacthera Manufacturing Agreement (defined below);

(ii)

cash installment payments of $50,000, which was received on January 15, 2025 and $25,000, which was received on July 1, 2025(offset by $1,421 paid by the Company to Nestlé on July 1, 2025 related to certain employment obligations assumed by SPN, as described below), conditioned on the Company’s material compliance with obligations under the Transition

Services Agreement (the “TSA”) (as described below) entered into at Closing between the Company and Nestlé Enterprises S.A., an affiliate of SPN, or NESA;

(iii)

prepayment of the $60,000 milestone payment tied to the achievement of worldwide annual net sales of the Product of $150,000 (the “First Sales Milestone”), which was paid 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) $125,000 tied to the achievement of worldwide annual net sales of the Product of $400,000 and (y) $150,000 tied to the achievement of worldwide annual net sales of the Product of $750,000, 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: (i) first, by set-off against all accrued interest on the Prepaid Milestone until the amount of such accrued interest has been paid 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, 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 (defined below), 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. The installment payment received on July 1, 2025 was offset by $1,421 paid by the Company to Nestlé on the same date related to certain employment obligations assumed by SPN with respect to the period ended as of the Closing Date.

The Company and SPN shared 50/50 in the net profit or net loss (the “Profit Sharing Payments”) achieved during the period from the date of Closing until December 31, 2025 (the “Profit Sharing Period”), 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 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, the Company reimbursed SPN for (i) certain payments under the exclusive license agreement between the Company and Memorial Sloan Kettering Cancer Center, (ii) certain costs incurred in connection with an ongoing post-marketing safety study of VOWST and (iii)80.1% of all rent and other costs due to the landlord under the lease for the Company’s Waltham facility.

At Closing, in exchange for a payment to be made by SPN to Bacthera AG, the Long Term Manufacturing Agreement, dated November 8, 2021 between the Company and Bacthera AG (the “Bacthera Manufacturing Agreement”) was terminated and each of Bacthera and Seres released one another from any and all losses, liabilities or other obligations arising thereunder with respect to the period ending at the Closing Date, including without limitation any milestone payments required to be paid to Bacthera thereunder.

On the Closing Date, the Company and SPN entered into a securities purchase agreement (the “Securities Purchase Agreement”) pursuant to which SPN purchased 714,285 shares (the “Shares”) of common stock at Closing, at a purchase price per share of $21.00, for an aggregate purchase price of $15,000. Under the terms of the Securities Purchase Agreement, SPN agreed not to sell or transfer the Shares for a period of six months after Closing, subject to certain customary exceptions. The Company agreed to register the resale of the Shares by SPN within 90 days of Closing. On October 1, 2024, the Company filed a registration statement to register the Shares, which became effective on October 11, 2024. 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 the Company’s outstanding shares of common stock, the Company has agreed to take such action within its control to include one individual designated by SPN in the slate of nominees recommended by the Company’s board of directors (or the applicable committee of the board of directors) to the Company’s stockholders for election to the board of directors at the applicable stockholder meeting. SPN designated Hans-Juergen Woerle, M.D., Ph.D. and on February 4, 2025, the Company’s board of directors appointed Dr. Woerle to the board as a Class III director, with a term expiring at the Company’s 2027 annual meeting of stockholders. The Securities Purchase Agreement contains customary representations and warranties and closing conditions.

On the Closing Date, the Company entered into a TSA with NESA, which provides for services to be performed by the Company in order to facilitate a transition of the business associated with the VOWST Business to NESA and its affiliates. The scope of the transition services includes 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. The Company provided the manufacturing services until December 31, 2025 and other services for the duration specified in the schedule to the TSA for each service. NESA paid the Company for certain fixed costs, including a monthly fixed fee and a variable per batch fee for preserved raw material suspension ("PRMS") manufacturing, and reimbursed the Company for certain costs of the transition services performed by the Company under the TSA, including labor. The know-how and other intellectual property generated in connection with the performance of the TSA will be owned by NESA with the Company having a non-exclusive license to such know-how and other intellectual property under the Cross-License Agreement. During the term of the TSA, the Company transferred the specifications for materials and documentation necessary to enable PRMS manufacturing services to a third party service provider designated by NESA. In the event of a material failure by the Company to deliver PRMS under the TSA, NESA had 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 the Company.

At the Closing Date, the Company entered into a cross-license agreement with SPN under which the Company granted 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 the Company that is not transferred to SPN pursuant to the Purchase Agreement. In the field of the treatment of Clostridioides difficile infections ("CDI") and recurrent CDI and associated complications (collectively, the “CDI Field”) the license to SPN under such Company patents and know-how will be exclusive to SPN for five years after Closing and co-exclusive between SPN and the Company following that five year period. The license from the Company to SPN is to issued Company 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. The Company also granted SPN an exclusive, perpetual, worldwide, fully paid-up license under issued Company 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 granted to the Company 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 TSA, for the Company’s products for use outside of the CDI Field, and after five years from Closing for Company 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 terminated and are of no further force or effect, except as contemplated by the Purchase Agreement. For example, on September 30, 2024, in connection with the Transaction, the 2016 License Agreement (the “2016 License Agreement”) with Nestec, Ltd., as succeeded by SPN (together with NHSc Rx License GmbH, their affiliates, and their subsidiaries “Nestlé”), and the 2021 License Agreement (the “2021 License Agreement”) with NHSc Pharma Partners, succeeded by NHSc Rx License GmbH (together with Société des Produits Nestlé S.A, their affiliates, and their subsidiaries “Nestlé”) were terminated upon mutual agreement of the parties, with provisions related to record retention, confidentiality obligations, indemnification obligations, intellectual property ownership, and any outstanding payment obligations surviving the termination of each of the 2016 License Agreement and 2021 License Agreement, respectively.

On the Closing Date, the parties entered into assignment and assumption of lease agreements (the “Assignment and Assumption Agreements”). Under the Assignment and Assumption Agreements, the Company assigned to SPN the Company’s rights in, to and under certain real property leases, and SPN assumed the liabilities related thereto.

On the Closing Date, the parties entered into an employee support agreement (the “Employee Support Agreement”). Under the Employee Support Agreement, among other things and subject to the terms and conditions therein, certain employees of the Company related to the VOWST Business who accepted employment with SPN or one of its designated affiliates provided the services they provided to the Company 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 or its designated affiliate’s next pay period following the Closing. SPN reimbursed the Company’s out of pocket costs in connection with such employees’ services, including certain compensation and benefits paid or provided to such employees pursuant to the terms of the Employee Support Agreement. All such employees were transferred to SPN as of December 31, 2024.

In connection with the Transaction, the Company fully retired its senior secured debt facility with Oaktree Capital Management. The Company intends to use the remaining proceeds to support the further advancement of SER-155 and the Company’s other wholly-owned cultivated live biotherapeutic candidates for medically vulnerable patient populations with potential to address large commercial opportunities.

The Company incurred certain significant costs relating to the Transaction, such as legal, accounting, financial advisory, printing and other professional services fees, as well as other customary payments. For the year ended December 31, 2024, these costs amounted to approximately $9,016, which is included within the net income (loss) from discontinued operations, net of tax line item on the Company's consolidated statements of operations.

Going Concern

The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants.

The accompanying consolidated financial statements have been prepared on a basis which assumes that the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the normal course of business. As of December 31, 2025, the Company had an accumulated deficit of $972,403 and cash and cash equivalents of $45,766.

The Company’s product candidates are in development, and will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to potential commercialization. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, or maintained, that any product candidate developed will obtain necessary government regulatory approval, or that any approved product will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales.

Primarily as a result of the costs associated with continuing the research and development efforts for SER-155 and the Company’s live biotherapeutics platform, the Company incurred a loss from operations of $93,971 and had operating cash outflows of $73,883, excluding the $75,000 installment payments received from Nestlé, for the year ended December 31, 2025. The Company expects that its operating losses and negative cash flows will continue for the foreseeable future. Based on the Company’s currently available cash resources, current and forecasted level of operations, and forecasted cash flows for the 12-month period subsequent to the date of issuance of these consolidated financial statements, the Company will require additional funding to support its ongoing operations and meet its obligations as they come due. These conditions raise substantial doubt about the Company’s ability to continue as a going concern.

The Company’s ability to continue as a going concern is dependent upon its ability to obtain the necessary financing to meet its obligations and repay its liabilities arising from normal business operations when they come due, and to generate profitable operations in the future. Management plans to provide for the Company’s capital requirements through financing or other strategic transactions, including potential business development transactions, and selling shares under the Company's at the market equity offering. There can be no assurance that the Company will be able to raise additional capital to fund operations with terms acceptable to the Company, or at all. Because certain elements of management’s plans to mitigate the conditions that raised substantial doubt about the Company’s ability to continue as a going concern are outside of the Company’s control, including the ability to raise capital through an equity or other financing, those elements cannot be considered probable according to Accounting Standards Codification (“ASC”) 205-40, Going Concern ("ASC 205-40"), and therefore cannot be considered in the evaluation of mitigating factors. As a result, management has concluded that substantial doubt exists about the Company’s ability to continue as a going concern for 12 months from the date these consolidated financial statements are issued. The accompanying consolidated financial statements do not include any adjustments that may result from the outcome of this uncertainty.

Reclassifications

Certain amounts in prior periods have been reclassified to reflect the impact of the discontinued operations treatment of the VOWST Business.

On April 21, 2025, the Company effected a 1-for-20 reverse stock split of the Company’s common stock. All share and per share amounts in the financial statements and notes thereto have been retroactively adjusted for all periods presented to give effect to this reverse stock split. The reverse stock split had no impact on the number of authorized shares or the par value of preferred and common stock. Therefore, the Company reclassified an amount equal to the reduction in the number of shares of common stock at par value to additional paid-in capital. No fractional shares were issued in connection with the reverse split, and stockholders who would otherwise be entitled to receive a fractional share instead received a cash payment equal to the fraction of a share of common stock in lieu of such fractional share. Proportionate adjustments were made to the number of shares authorized under the Company’s equity incentive plans, the number of shares subject to any award or purchase right under the Company’s equity incentive plans, and the exercise price or purchase price with respect to any stock option award or purchase right under the Company’s equity incentive plans. See Note 7, Stock and Stock-Based Awards, for further information.

The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly owned subsidiaries after elimination of all intercompany accounts and transactions.

Summary of Significant Accounting Policies

Discontinued Operations

The Company accounted for the sale of its VOWST Business in accordance with ASC 205 Discontinued Operations and ASU No. 2014-08, Reporting of Discontinued Operations and Disclosures of Disposals of Components of an Entity. The Company followed the held-for-sale criteria as defined in ASC 205. ASC 205 requires that a component of an entity that has been disposed of or is classified as held for sale and has operations and cash flows that can be clearly distinguished from the rest of the entity be reported as assets held for sale and discontinued operations. In the period a component of an entity has been disposed of, the results of operations for the periods presented are reclassified into separate line items in the consolidated statements of operations. In the period a discontinued operation is classified for sale, the assets and liabilities of the discontinued operation are also reclassified into separate line items on the related consolidated balance sheets for the periods presented.

Due to the sale of the VOWST Business during the third quarter of 2024 (see Note 3, Discontinued Operations and TSA), in accordance with ASC 205, Discontinued Operations, the Company has classified the results of the VOWST Business as discontinued operations in its consolidated statements of operations and cash flows for all periods presented. All amounts included in the notes to the consolidated financial statements relate to continuing operations unless otherwise noted.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting periods. In these consolidated financial statements, the Company uses estimates and assumptions related to the accrual of research and development expenses. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.

Restricted Cash

The Company held restricted cash of$8,668 as of December 31, 2025 and 2024, which represents cash held for the benefit of the landlord for certain of the Company’s leases. The Company has classified the restricted cash as long-term on its consolidated balance sheets as the underlying leases are greater than 1 year.

Cash, cash equivalents and restricted cash were comprised of the following (in thousands):

Concentration of Credit Risk

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash balances at financial institutions in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the useful life of the asset, which are as follows:

Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations.

Impairment of Long-Lived Assets

Long-lived assets consist of property and equipment and right-of-use assets associated with our lease agreements. All of the Company's long-lived assets are to be held and used and have definitive lives and accordingly are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset or asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset or asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. For the years ended December 31, 2025, 2024 and 2023, the Company recorded an impairment loss on long-lived assets of $0, $3,267 and $0, respectively.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development expenses include salaries, stock-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including allocated facility-related expenses and external costs of outside vendors engaged to conduct both preclinical studies and clinical trials, and beginning in the fourth quarter of 2024 certain costs of fulfilling the Company's obligations under the TSA which are reimbursable by Nestlé.

Research Contract Costs and Accruals

The Company has entered into various research and development contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs based on reporting provided by third parties, typically contract research organizations. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued and prepaid balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Patent Costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.

Accounting for Stock-Based Compensation

The Company measures all stock options and other stock-based awards granted to employees, non-employees, and directors based on the fair value on the date of the grant and recognizes compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues stock options, restricted stock units and restricted stock awards with only service-based vesting conditions and records the expense for these awards using the straight-line method. For stock options or restricted stock units issued with performance-based vesting conditions, the stock compensation expense related to these awards is recognized based on the grant date fair value when achievement of the performance condition is deemed probable.

The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive income (loss) in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified.

The Company accounts for forfeitures of stock-based awards as they occur rather than applying an estimated forfeiture rate to stock-based compensation expense.

The fair value of each stock option grant is estimated on the date of grant using the Black- Scholes option-pricing model. The Company estimates its expected common stock volatility based on its historical common stock volatility for the same time period. The Company uses the simplified method prescribed by Securities and Exchange Commission Staff Accounting Bulletin No. 107, Share-Based Payment, to calculate the expected term of options granted to employees, non-employees and directors. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

Grant Revenue

The Company generates revenue from government contracts that reimburse the Company for certain allowable costs for funded projects. For contracts with government agencies, when the Company has concluded that it is the principal in conducting the research and development expenses, and where the funding arrangement is considered central to the Company’s ongoing operations, the Company classifies the recognized funding received as revenue.

The Company has concluded to recognize funding received as revenue, rather than as a reduction of research and development expenses, because the Company is the principal in conducting the research and development activities and these contracts are central to its ongoing operations. Revenue is recognized as the qualifying expenses related to the contracts are incurred. Revenue recognized upon incurring qualifying expenses in advance of receipt of funding is recorded in the Company’s consolidated balance sheet as accounts receivable. The related costs incurred by the Company are included in research and development expense in the Company’s consolidated statements of operations and comprehensive loss.

Income Taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense.

The Company applies ASC 740-10, Accounting for Uncertain Tax Positions. The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Segment Reporting

The Company manages its operations as a single operating segment for the purposes of assessing performance and making operating decisions, and thus reports as a single reportable segment. The Company’s singular focus is on developing live biotherapeutics for medically vulnerable patient populations to prevent bacterial bloodstream and antimicrobial resistant (AMR) infections as well as to treat GI-related immune diseases. Revenue to date has been generated solely through the Company's agreements with its collaborators, all of which has been earned in the United States. All tangible assets are held in the United States.

Comprehensive Income (Loss)

Comprehensive income (loss) includes net income (loss) as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the year ended December 31, 2023, other comprehensive income consisted of changes in unrealized gains from available-for-sale investments and a currency translation adjustment.

Net Income (Loss) per Share

Basic net income (loss) per share is computed using the weighted average number of common shares outstanding during the period. Diluted net income (loss) per share is computed using the sum of the weighted average number of common shares outstanding during the period and, if dilutive, the weighted average number of potential shares of common stock, including the assumed exercise of stock options and unvested restricted stock. The Company applies the two-class method to calculate its basic and diluted net loss per share attributable to common stockholders. The two-class method is an earnings allocation formula that treats a participating security as having rights to earnings that otherwise would have been available to common stockholders. However, the two-class method does not impact the net loss per share of common stock for periods in which the Company is in a net loss position.

The Company’s restricted stock awards entitle the holder of such awards to dividends declared or paid by the board of directors, regardless of whether such awards are unvested, as if such shares were outstanding common shares at the time of the dividend. However, the unvested restricted stock awards are not entitled to share in the residual net assets (deficit) of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.

Leases

In accordance with ASC 842, Leases, the Company determines if an arrangement is or contains a lease at inception. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company classifies leases at the lease commencement date as operating or finance leases and records a right-of-use asset and a lease liability on the consolidated balance sheets for all leases with an initial lease term of greater than 12 months. Leases with an initial term of 12 months or less are not recorded on the balance sheets, but payments are recognized as expense on a straight-line basis over the lease term. The Company has elected not to record a right-of-use asset or lease liability for leases with terms of 12 months or less.

A lease qualifies as a finance lease if any of the following criteria are met at the inception of the lease: (i) there is a transfer of ownership of the leased asset to the Company by the end of the lease term, (ii) the Company holds an option to purchase the leased asset that it is reasonably certain to exercise, (iii) the lease term is for a major part of the remaining economic life of the leased asset, (iv) the present value of the sum of lease payments equals or exceeds substantially all of the fair value of the leased asset, or (v) the nature of the leased asset is specialized to the point that it is expected to provide the lessor no alternative use at the end of the lease term.

The Company enters into contracts that contain both lease and non-lease components. Non-lease components may include maintenance, utilities, and other operating costs. The Company combines the lease and non-lease components of fixed costs in its lease arrangements as a single lease component. Variable costs, such as utilities or maintenance costs, are not included in the measurement of right-of-use assets and lease liabilities, but rather are expensed when the event determining the amount of variable consideration to be paid occurs.

Finance and operating lease assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term using the discount rate implicit in the lease. If the rate implicit is not readily determinable, the Company utilizes an estimate of its incremental borrowing rate based upon the available information at the lease commencement date. Operating lease assets are further adjusted for prepaid or accrued lease payments. Operating lease payments are expensed using the straight-line method as an operating expense over the lease term. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Finance lease assets are amortized to depreciation expense using the straight-line method over the shorter of the useful life of the related asset or the lease term. Finance lease payments are bifurcated into (i) a portion that is recorded as imputed interest expense and (ii) a portion that reduces the finance liability associated with the lease.

Right-of-useassets and lease liabilities are reassessed and remeasured when amendments to the terms of the lease agreement require reassessment and remeasurement of the lease payments and other inputs to the calculation of right-of-use assets and lease liabilities. The Company accounts for remeasurements and modifications to lease liabilities using the present value of remaining lease payments and estimated incremental borrowing rate at the date of remeasurement. The adjustment to the lease liability is recognized as again or loss in operating expenses, or as an adjustment to the right-of-use asset, as appropriate, based on the terms and conditions within the lease that are amended.

Recently Adopted Accounting Pronouncements

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures which requires public entities to disclose specific categories in the effective tax rate reconciliation, as well as expanded disclosures on income taxes paid by jurisdictions. ASU 2023-09 is effective for fiscal years beginning after December 15, 2024, with early adoption permitted. The Company adopted this standard and applied the disclosure requirements on a prospective basis effective for the annual reporting period ended December 31, 2025. There was no impact on the Company’s consolidated financial statements and additional required disclosures have been included in Note 11, Income Taxes.

Recently Issued Accounting Pronouncements

In November 2024, the FASB issued ASU 2024-03, Disaggregation of Income Statement Expenses (Topic 220), which requires disclosure in the notes to financial statements about specific types of expenses included in the expense captions presented on the face of the statement of operations. The requirements of the ASU are effective for annual periods beginning after December 15, 2026, and for interim periods beginning after December 15, 2027, with early adoption permitted. The requirements will be applied prospectively with the option for retrospective application. The Company is currently evaluating the impact related to the adoption of ASU 2024-03 on its financial statement disclosures.

In December 2025, the FASB issued ASU 2025-10, Government Grants (Topic 832): Accounting for Government Grants Received by Business Entities, which standardizes the accounting for government grants and distinguishes between a grant related to an asset and a grant related to income. The requirements of the ASU are effective for annual periods beginning after December 15, 2028, and for interim periods within those annual periods, with early adoption permitted. The requirements can be applied using a modified prospective or a modified retrospective approach. The Company does not expect the impact of ASU 2025-10 to be material to its financial statement disclosures as it is consistent with the Company's current accounting policy for government grants.

3. Discontinued Operations and TSA

On September 30, 2024, the Company completed the sale of its VOWST Business to SPN. The Company has determined the sale of the VOWST Business represents a strategic shift that will have a major effect on its business and therefore met the criteria for classification as discontinued operations on September 30, 2024. Accordingly, the VOWST Business is reported as discontinued operations in accordance with ASC 205-20, Discontinued Operations. The related assets and liabilities of the VOWST Business are classified as assets and liabilities of discontinued operations in the consolidated balance sheets and the results of operations from the VOWST Business as discontinued operations in the consolidated statements of operations. Applicable amounts in prior years have been recast to conform to this discontinued operations presentation. The Company recognized a gain on the sale of the VOWST Business upon closing.

As of December 31, 2025 and 2024, there wereno assets or liabilities of discontinued operations.

The following table presents the gain on the sale of the VOWST Business as of December 31, 2024, pursuant to the Purchase Agreement:

[1] The upfront payment consists of$100,000, less $17,857 owed by the Company to an affiliate of SPN under the prior license agreement between the Company and the SPN affiliate, less approximately $2,355 in satisfaction of costs due under the Bacthera Manufacturing Agreement.

For the year ended December 31, 2024, the gain from sale of the VOWST Business, net of tax of $146,707 was included in the net income (loss) from discontinued operations, net of tax line item of the Company’s consolidated statements of operations and comprehensive income (loss). While the Company has net income from discontinued operations for the year ended December 31, 2024, the Company realized a tax loss for the full year ended December 31, 2024, for which it is more likely than not that the Company will not realize a benefit. The Company has recorded a full valuation allowance against its net deferred tax assets as of December 31, 2025, 2024 and 2023.

The following table presents the financial results of the discontinued operations:

In accordance with ASC 205-20, only expenses specifically identifiable and related to a business to be disposed may be presented in discontinued operations. As such, the research and development and general and administrative expenses in discontinued operations include corporate costs incurred directly to solely support the VOWST Business.

The Company also entered into a Transition Services Agreement (“TSA”) with NESA, an affiliate of SPN, in connection with the Transaction, through which the Company provided certain manufacturing services until December 31, 2025, and other transition services, for the duration specified in the schedule to the TSA for each service. For the years ended December 31, 2025 and 2024, the Company recognized $13,311 and $6,292 of TSA reimbursement income in other income in the Company’s consolidated statements of operations and comprehensive income. For theyears ended December 31, 2025 and 2024, the Company incurred $6,544 and $3,532 of expenses related to manufacturing services and $3,592 and $3,136 of TSA labor and passthrough expenses to support the transition services, including finance and accounting, information technology, human resources, operations, and other services.

For the years ended December 31, 2025 and 2024, $14,897 and $3,724 was billed to NESA related to transition services performed by the Company, and the Company received $91,605 and $1,656 from NESA during the periods including the first installment payment of $50,000 received in January 2025 and the second installment payment of $25,000 received in July 2025 which were conditioned on the Company’s material compliance with obligations under the TSA. The $75,000 of installment payments were recognized in Gain on sale of VOWST Business within continuing operations in the Company’s consolidated statements of operations and comprehensive income for theyear ended December 31, 2025 as the gain was realizable. As of December 31, 2025 and 2024, the Company had $360 and $2,068 in accounts receivable due from SPN - related party in the Company’s consolidated balance sheets.

The Company has estimated costs associated with certain accrued liabilities due to SPN - related party as a loss contingency in accordance with ASC 450, Contingencies. These contingent liabilities are presented as Accrued Liabilities due to SPN - related party from continuing operations on the consolidated balance sheets as of December 31, 2025 and December 31, 2024 and consist of the following (in thousands):

The contingent liabilities accrued on the Company's consolidated balance sheets are remeasured at December 31, 2025 based on i) cash payments made by the Company to reduce the accrued liabilities due to SPN - related party and ii) revised estimates of the total remaining liabilities due to SPN - related party. For the years ended December 31, 2025 and 2024, the Company recognized a gain on sale of VOWST Business of $5,685 and $5,684, respectively, as a result of the change in the accrued liabilities due to SPN - related party.

The Company has excluded from its consolidated balance sheets the effects of certain milestone payments received by the Company after the Product has achieved net sales-based milestones. These contingent receivables will be recognized as a gain contingency, in accordance with ASC 450, Contingencies, in continuing operations in the period when the contingencies are resolved.

The cash flows related to discontinued operations have not been segregated and are included in the consolidated statements of cash flows. There were no cash flows related to discontinued operations for the year ended December 31, 2025. For the years ended December 31, 2024 and 2023, capital expenditures related to the VOWST Business were $112 and $2,272, respectively. Depreciation expense related to the VOWST Business for the same periods was $989 and $2,019, respectively. Non-cash operating lease costs related to the VOWST Business for the years ended December 31,2024 and 2023 were $1,447 and $2,123, respectively, while the share based compensation expense for the same periods were $1,884 and $2,773, respectively. The collaboration loss sharing (related party) related to the VOWST Business was $0 and $5,158 for the years ended December 31,2024 and 2023, respectively. Excluding the gain of $146,707 recognized on the sale of the VOWST Business presented in the consolidated statements of cash flows for theyear ended December 31, 2024, there were no other material operating or investing non-cash items related to the VOWST Business for any period presented.

4. Property and Equipment, Net

Property and equipment, net consisted of the following (in thousands):

Depreciation and amortization expense was$4,133,$5,468 and$6,243 for the years ended December 31, 2025, 2024 and 2023, respectively, which includes amounts related to both continuing and discontinued operations. During the years ended December 31, 2025 and 2024, the Company disposed of certain assets with a cost basis of $734 and $679, respectively, and a net book value of $18 and $0, respectively. In addition, during the year ended December 31, 2024, the Company recorded an impairment loss of $1,536 related to leasehold improvements at one of the Company's locations for which impairment indicators were determined to exist as of December 31, 2024. See Note 6, Leases, for further details.

5. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:

6. Leases

The Company leases real estate, primarily laboratory, office and manufacturing space. The Company’s leases have remaining terms ranging from approximately three toseven years. Certain leases include one or more options to renew, exercisable at the Company’s sole discretion, with renewal terms that canextend the lease from approximately five years toten years. The Company evaluated the renewal options in its leases to determine if it was reasonably certain that the renewal option would be exercised, given the Company’s current business structure, uncertainty of future growth, and the associated impact to real estate, the Company concluded that it is not reasonably certain that any renewal options would be exercised. Therefore, the operating lease assets and operating lease liabilities only contemplate the initial lease terms. All the Company’s leases qualify as operating leases.

In January 2024, the Company entered into a sublease agreement with an unrelated third party to sublease a portion of its office and laboratory space in Cambridge, Massachusetts. The term of the sublease agreement commenced in March 2024 and ends on January 13, 2030. The Company will receive lease payments over the sublease term totaling $10,400. The sublessee is obligated to pay all real estate taxes and costs related to the subleased premises, including cost of operations, maintenance, repair, replacement and property management. Sublease income is recorded as Other (expense) income, net in the Company’s consolidated statements of operations and comprehensive income (loss).

During the year ended December 31, 2024, the Company identified an indicator of impairment of its donor collection facility in Cambridge, Massachusetts, as the facility is no longer being used by the Company and is being marketed for sublease. The Company determined that this represents a significant adverse change in the extent in which the long-lived asset was being used. The Company determined that the location contains multiple asset groups for the purpose of the long-lived asset impairment assessment. The Company concluded that the carrying value of each asset group was not recoverable as it exceeded the future net undiscounted cash flows that are expected to be generated from the assets within the asset group. In the first quarter of 2024, the Company recognized an impairment loss of $3,267, consisting of $1,731 on the operating lease right-of-use asset and $1,536 on the leasehold improvements. $2,727 of the total impairment loss is included in research and development expenses and the remaining $540 is included in general and administrative expenses in the accompanying consolidated statements of operations and comprehensive income (loss).

The following table summarizes the presentation in the Company’s consolidated balance sheets of its operating leases (in thousands):

The following table summarizes the effect of lease costs in the Company’s consolidated statements of operations and comprehensive income (loss) (in thousands):

During the years ended December 31, 2025, 2024, and 2023, the Company made cash payments for operating leases of$19,442,$17,330 and$15,656, respectively.

As of December 31, 2025, future payments of operating lease liabilities are as follows (in thousands):

As of December 31, 2025, the weighted average remaining lease term was 6.07 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 13%. As of December 31, 2024, the weighted average remaining lease term was 6.98 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 13%.

7. Stock and Stock-Based Awards

On July 1, 2015, in connection with the closing of the initial public offering of the Company’s common stock (“IPO”), the Company effected its Restated Certificate of Incorporation, which authorizes the Company to issue 10,000,000 shares of preferred stock, $0.001 par value per share.

On April 10, 2025, at the Company's 2025 annual meeting of stockholders (the “2025 Annual Meeting”), stockholders approved an amendment to the Company’s Restated Certificate of Incorporation in order to effect a reverse stock split of all outstanding shares of the Company's common stock. On April 21, 2025, the Company effected a 1-for-20 reverse stock split of its common stock. The reverse stock split had no impact on the number of authorized shares or the par value of preferred and common stock. As of the effective time of the reverse stock split, the number of shares of common stock issuable upon exercise, vesting or settlement of outstanding awards, the exercise price of all outstanding options and any stock price vesting goals with respect to any outstanding awards under the Company’s equity plans (including the 2025 Plan, as defined below) was proportionately adjusted (and rounded down to the nearest whole share in the case of shares and up to the nearest whole cent in the case of exercise prices, as applicable) based on the 1-for-20 ratio. In addition, the number of shares available for future issuance and any share‑based award limits under the Company’s equity plans were proportionately reduced based on the 1-for-20 ratio. Trading of the Company's common stock on The Nasdaq Global Select Market commenced on a split-adjusted basis on April 22, 2025.

On September 30, 2024, the Company entered into the Securities Purchase Agreement with SPN, pursuant to which SPN purchased 714,285 shares at the Closing at a purchase price per share of $21.00, for an aggregate purchase price of $15,000. Under the terms of the Securities Purchase Agreement, SPN has agreed not to sell or transfer the shares for a period of six months after Closing, subject to certain customary exceptions. The Company agreed to register the resale of the Shares by SPN within 90 days of Closing. On October 1, 2024, the Company filed a registration statement to register the Shares, which became effective on October 11, 2024. 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 the Company's outstanding shares of common stock, the Company has agreed to take such action within its control to include one individual designated by SPN in the slate of nominees recommended by the Company's board of directors (or the applicable committee of the board) to the Company's stockholders for election to the board at the applicable stockholder meeting. The Securities Purchase Agreement contains customary representations and warranties and closing conditions. The aggregate fair value of $13,516 for the common stock issued to SPN was recorded in equity, with the remaining $1,484 cash received from SPN under the Securities Purchase Agreement allocated to the consideration transferred for the VOWST Business.

On February 22, 2024, the Company’s board of directors adopted a resolution to amend the Restated Certificate of Incorporation, subject to stockholder approval, by increasing the number of authorized shares of the Company’s Common Stock from 240,000,000 shares to 360,000,000 shares (the “Share Increase Amendment”). At the Company’s annual meeting of stockholders held on April 4, 2024, the Company’s stockholders approved the Share Increase Amendment. On April 5, 2024, the Company amended its Restated Certificate of Incorporation to reflect the Share Increase Amendment.

In May 2021, the Company entered into a Sales Agreement (the“Sales Agreement”) with Cowen and Company, LLC ("Cowen") to sell shares of the Company’s common stock, with aggregate gross sales proceeds of up to $150,000, from time to time, through an "at-the-market" equity offering program (“ATM”) under which Cowen acts as sales agent. During the year ended

December 31, 2025, the Company sold 739,545 shares of common stock under the 2021 Sales Agreement, at an average price of approximately $18.48 per share, raising aggregate net proceeds of approximately $13,167 after deducting an aggregate commission of approximately 3% and other issuance costs. During the year ended December 31, 2024, the Company sold 1,030,846 shares of common stock under the 2021 Sales Agreement, at an average price of approximately $23.67 per share, raising aggregate net proceeds of approximately $23,530 after deducting an aggregate commission of approximately 3% and other issuance costs.

2015 and 2025 Incentive Award Plans

On June 16, 2015, the Company’s stockholders approved the 2015 Incentive Award Plan (the “2015 Plan”), which became effective on June 25, 2015. The 2015 Plan was subsequently amended on December 14, 2022, and provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. The number of shares initially reserved for issuance under the 2015 Plan was the sum of (i) 110,000 shares of common stock and (ii) the number of shares subject to awards outstanding under the 2012 Plan that expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by the Company on or after the effective date of the 2015 Plan. In addition, the number of shares of common stock that may be issued under the 2015 Plan was subject to increase on the first day of each calendar year, beginning in 2016 and ending in 2025, equal to the lesser of (i)4% of the number of shares of the Company’s common stock outstanding on the last day of the preceding applicable calendar year and (ii) an amount determined by the Company’s board of directors.

On April 10, 2025, the Company's stockholders approved the 2025 Incentive Award Plan (the “2025 Plan”) as an amendment and restatement of the Seres Therapeutics, Inc. 2015 Incentive Award Plan. The amendment, among other things, authorized the issuance of 2,230,243 shares of the Company’s common stock for awards under the 2025 Plan, which includes 1,750,493 shares previously authorized for issuance under the 2015 Plan plus an increase of 479,750 shares (in each case, which amounts reflect the 1-for-20 reverse stock split), and extended the term of the 2025 Plan to March 3, 2035, the tenth anniversary of the approval of the 2025 Plan by the Company’s board of directors.

Stock awards granted under the 2025 Plan generally vest over four years and expire afterten years, although options have been granted with vesting terms less than four years. As of December 31, 2025, there were 740,410 shares available for future grant under the 2025 Plan.

2015 Employee Stock Purchase Plan

On June 16, 2015, the Company’s stockholders approved the 2015 Employee Stock Purchase Plan (the “ESPP”), which became effective on June 25, 2015. A total of 18,250 shares of common stock were reserved for issuance under the ESPP. In addition, the number of shares of common stock that may be issued under the ESPP automatically increase on the first day of each calendar year, beginning in 2016 and ending in 2025, by an amount equal to the lesser of (i)20,000 shares, (ii)1% of the number of shares of the Company’s common stock outstanding on the last day of the applicable preceding calendar year and (iii) an amount determined by the Company’s board of directors. Offering periods under the ESPP will commence when determined by the plan administrator. During the year ended and as of December 31, 2025, there were 17,839 shares issued and 106,064 shares were reserved and available for issuance under the ESPP, respectively.

The ESPP provides that eligible employees may contribute up to 15% of their eligible earnings toward the semi-annual purchase of the Company's common stock. Purchase rights issued under the ESPP are intended to be qualified under Section 423 of the Internal Revenue Code of 1986, as amended ("IRC"). The employee's purchase price is derived from a formula based on the closing price of the common stock on the first day of the offering period versus the closing price on the date of purchase (or, if not a trading day, on the immediately preceding trading day). The offering period under the ESPP has a duration ofsix months, and the purchase price with respect to each offering period beginning on or after such date is, until otherwise amended, equal to 85% of the lesser of (i) the fair market value of the Company's common stock at the commencement of the applicable six-month offering period or (ii) the fair market value of the Company's common stock on the purchase date.

2022 Employment Inducement Award Plan

On December 14, 2022, the Company’s board of directors approved the 2022 Employment Inducement Award Plan (the "2022 Plan"), which became effective on such date without stockholder approval pursuant to Rule 5635(c)(4) of The Nasdaq Stock Market LLC listing rules (“Rule 5635(c)(4)”). The 2022 Plan provides for the grant of nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock- or cash-based awards. In accordance with Rule 5635(c)(4), awards under the 2022 Plan may only be made to a newly hired employee who has not previously been a member of our board of directors, or an employee who is being rehired following a bona fide period of non-employment by us as a material inducement to the employee’s entering into employment with us. A total of 125,000 shares of common stock were reserved for issuance under the 2022 Plan. Any shares subject to awards previously granted under the 2022 Plan that expire, terminate or are otherwise surrendered, canceled, or forfeited in any case, in a manner that results in the Company acquiring the shares covered by the award at a price not greater than the price (as adjusted to reflect any equity restructuring) paid by the Participant for such shares or not issuing any shares covered by the award, the unused shares covered by the award will again be available for award grants under the 2022 Plan.

As of December 31, 2025, there were 86,644 shares available for future grant under the 2022 Plan.

Stock Options

The following table summarizes the Company’s stock option activity for the year ended December 31, 2025:

In February 2024, the Company approved a repricing of certain stock option awards to reduce the original exercise price to the Company’s current fair market value as of February 12, 2024 (the “Repricing”). The Repricing became effective 18 months from the approval date, or August 2025. The remaining terms and conditions of each option affected by the Repricing remained the same, including the expiration date, vesting commencement date, vesting schedule and any vesting acceleration. As the Repricing was retrospective to February 2024, the weighted average exercise price for stock options outstanding as of December 31, 2024 in the table above has been adjusted to reflect the Repricing. The Repricing was accounted for as a modification, and an immaterial amount of incremental fair value is being recognized from the date the Repricing was approved over the remaining vesting term of the options.

The weighted average grant-date fair value of stock options granted during the years ended December 31, 2025, 2024, and 2023 was$13.30,$18.58, and$90.37 per share, respectively. The total intrinsic value of stock options exercised during the years ended December 31, 2025, 2024, and 2023 was$98,$0, and$438, respectively.

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock.

During the year ended December 31, 2021, the Company granted performance-based stock options to employees for the purchase of an aggregate of 28,100 shares of common stock with a grant date fair value of $110.60 per share. These stock options are exercisable only upon achievement of specified performance targets. In April 2023, the performance target associated with 50% of the performance-based stock options was achieved. Accordingly, the Company recorded $0, $8 and $2,051 of compensation expense during the years ended December 31, 2025, 2024 and 2023, respectively, with respect to these performance-based stock options, which represents a cumulative catch-up from the grant date through the achievement of the performance targets, and vesting of the remaining 50% of the options beginning in April 2023. The remaining compensation expense associated with these performance-based stock options was recognized as of April 2024, for all such options for which ongoing performance targets were achieved and service requirements were met.

During the three months ended March 31, 2024, the Company granted stock options to certain executives for the purchase of an aggregate of 127,500 shares of common stock. These awards will vest only to the extent that the 30-day trailing simple average public market closing price of the Company's common stock reaches certain price thresholds. These awards have an exercise price of $22.00 and vest and become exercisable when the market conditions are satisfied or, if later, on the first anniversary of the grant date. These awards expire 10 years from the date of grant. The fair value of these market-based stock options was estimated using a Monte Carlo valuation method. During theyears ended December 31, 2025 and 2024, the Company recognized $641 and $775 of compensation expense related to these awards.

Restricted Stock Units

The Company has granted restricted stock units with service-based vesting conditions ("RSUs") and restricted stock units with performance-based vesting conditions ("PSUs"). RSUs and PSUs represent the right to receive shares of common stock upon meeting specified vesting requirements. Restricted stock units may not be sold or transferred by the holder and vest according to the vesting conditions of each award. The table below summarizes the Company’s RSU and PSU activity for the year ended December 31, 2025:

During the years ended December 31, 2025, 2024, and 2023, the Company granted 79,846,75,066 and 154,904 RSUs, respectively. RSUs generally vest over four years, with 25% vesting afterone year, and the remaining 75% vesting quarterly over the next 3 years, subject to continued service to the Company through the applicable vesting date. PSUs vest according to the performance requirements of the awards, generally when the Company has determined that the specified performance targets have been achieved.

During the year ended December 31, 2023, the Company granted PSUs to employees covering an aggregate of 66,135 shares of common stock with a grant date fair value of $110.00. These PSUs begin to vest ratably only upon achievement of specified performance targets, which were achieved in April 2023. Accordingly, the Company recorded $0, $792 and $4,293 in compensation expense during the years ended December 31, 2025, 2024, and 2023 respectively, with respect to these PSUs.

The aggregate intrinsic value of RSUs, including PSUs for which the performance conditions have been met, that vested during the years ended December 31, 2025, 2024 and 2023 was$1,903,$1,899, and$4,729, respectively.

Retention Awards

In September 2025, the Company issued retention awards to employees of the Company in the form of RSUs covering 68,596 shares of common stock with a grant date fair value of $18.93 per share. The retention RSUs fully vested on November 15, 2025 subject to the employee's continued employment with the Company through such date. The compensation expense associated with these awards was recognized ratably over the vesting period. For theyear ended December 31, 2025, the Company recognized $1,299 in compensation expense with respect to the retention RSUs.

In November 2023, as part of the corporate restructuring described in Note 9, Restructuring, the Company issued retention awards to employees of the Company in the form of RSUs, which vested as to the first tranche on August 15, 2024 and as to the second tranche on May 15, 2025, subject to remaining actively employed with the Company through such date. The compensation expense associated with these awards was recognized ratably over the vesting period. For the years ended December 31, 2025, 2024, and 2023, the Company recognized $163, $655 and $92, respectively, in compensation expense with respect to the retention awards.

Stock-based Compensation Valuation

The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors were as follows, presented on a weighted average basis:

The Company estimates the fair value of rights to acquire common stock under the ESPP using a Black-Scholes valuation model on the date of grant and the straight-line attribution approach to recognize the expense. The assumptions that the Company used to determine the fair value of rights to acquire common stock under the ESPP were as follows, presented on a weighted average basis:

Stock-based Compensation

The Company recorded stock-based compensation expense related to stock options and restricted stock units in the following expense categories of its consolidated statements of operations and comprehensive income (loss):

As of December 31, 2025, the Company had an aggregate of$9,986 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 3.2 years.

8. Net Income (Loss) per Share

Basic and diluted net income (loss) per share attributable to common stockholders was calculated as follows (in thousands, except share and per share data):

The Company's potential dilutive securities include stock options, unvested restricted common stock and shares issuable under the 2015 Employee Stock Purchase Plan. The effect of dilutive securities was calculated using the treasury stock method. The anti-dilutive potential common stock equivalents for the year ended December 31, 2025 were excluded from the computation of diluted net income per share attributable to common stockholders because those stock options to purchase common stock and restricted stock units had an anti-dilutive impact due to the assumed proceeds per share using the treasury stock method being greater than the average fair value of the Company’s common shares for those periods. For that same period, the warrants to purchase common stock were excluded because the exercise price of the Tranche A Warrants is greater than the average fair value of the Company’s common shares. The anti-dilutive potential common stock equivalents for the years ended December 31, 2024 and 2023 were excluded from the computation of diluted net loss per share attributable to common stockholders because those stock options to purchase common stock, restricted stock units, and shares issuable under employee stock purchase plan had an anti-dilutive impact as the Company reported a net loss from continuing operations attributable to common stockholders for those periods

The Company utilizes the control number concept in the computation of diluted earnings per share to determine whether potential common stock equivalents are dilutive. The control number used is income (loss) from continuing operations. The control number concept requires that the same number of potentially dilutive securities applied in computing diluted earnings per share from continuing operations be applied to all other categories of income or loss, regardless of their anti-dilutive effect on such categories. Since the Company had a net loss from continuing operations for all periods in which discontinued operations is presented, no dilutive effect has been recognized in the calculation of income from discontinued operations per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same for the years ended December 31, 2024 and 2023.

9. Restructuring

On September 23, 2025, the Company announced that it implemented cost reduction actions, including decreasing its workforce by approximately 25%. During theyear ended December 31, 2025, the Company incurred approximately $1,027 in restructuring costs, primarily related to severance costs. These costs were paid out in the fourth quarter of 2025.

On November 2, 2023, the Company announced a restructuring plan to prioritize the commercialization of VOWST and the completion of the SER-155 Phase 1b study, while significantly reducing costs and supporting longer-term business sustainability. The restructuring plan included (i) a reduction of the Company’s workforce by approximately 41% across the organization, resulting in the elimination of approximately 160 positions; (ii) significantly scaling back all non-partnered research and development activities other than the completion of the SER-155 Phase 1b study; and (iii) reducing general and administrative expenses, including consolidating office space.

During the year ended December 31, 2023, the Company recognized a restructuring charge of $5,606, which was incurred entirely in the fourth quarter of 2023, and which represents all restructuring charges expected to be incurred. $3,481 of the total restructuring charges was included in research and development expenses and the remaining $2,125 in general and administrative expenses in the accompanying consolidated statements of operations and comprehensive income (loss) for the year ended December 31, 2023. Restructuring charges included approximately $5,345 of employee related termination costs in the form of salary continuation and cash severance payments, and $261 related to the acceleration of vesting of certain previously granted RSUs and PSUs.

The unpaid restructuring charge included in accrued expenses and other current liabilities in the Company’s consolidated balance sheets was $0 and $20 for the years ended December 31, 2025 and 2024, respectively.

10. Commitments and Contingencies

Leases

Refer to Note 6, Leases, for discussion of the commitments associated with the Company’s lease portfolio.