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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q

(Mark One)


☒	QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended September 30, 2025


☐	TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from to

Commission File Number: 001-37465

Seres Therapeutics, Inc.

(Exact name of registrant as specified in its charter)


Delaware		27-4326290
(State or other jurisdiction of incorporation or organization)		(I.R.S. Employer Identification No.)

101 Cambridgepark Drive Cambridge, MA		02140
(Address of principal executive offices)		(Zip Code)

(617) 945-9626

(Registrant’s telephone number, including area code)

Not Applicable

(Former name, former address and former fiscal year, if changed since last report)

Securities registered pursuant to Section 12(b) of the Act:

     Title of each class

     Trading Symbol(s)

     Name of each exchange on which registered

     Common Stock, par value $0.001

     MCRB

      The Nasdaq Stock Market LLC 
(Nasdaq Global Select Market)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ☒ No ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.


Large accelerated filer	☐	Accelerated filer	☒
Non-accelerated filer	☐	Smaller reporting company	☒
Emerging growth company	☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐


	Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes ☐ No ☒

As of October 31, 2025, the registrant had 9,046,519 shares of common stock, $0.001 par value per share, outstanding.

Seres Therapeutics, Inc.

INDEX


		Page

PART I – FINANCIAL INFORMATION
Item 1. Condensed Consolidated Financial Statements (unaudited)		5
Condensed Consolidated Balance Sheets as of September 30, 2025 and December 31, 2024		5
Condensed Consolidated Statements of Operations and Comprehensive Income for the three and nine months ended September 30, 2025 and 2024		6
Condensed Consolidated Statements of Stockholders’ Equity (Deficit) for the nine months ended September 30, 2025 and 2024		7
Condensed Consolidated Statements of Cash Flows for the nine months ended September 30, 2025 and 2024		9
Notes to Condensed Consolidated Financial Statements		10
Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations		25
Item 3. Quantitative and Qualitative Disclosures About Market Risk		43
Item 4. Controls and Procedures		43

PART II – OTHER INFORMATION
Item 1. Legal Proceedings		44
Item 1A. Risk Factors		44
Item 2. Unregistered Sales of Equity Securities and Use of Proceeds		83
Item 3. Defaults Upon Senior Securities		83
Item 4. Mine Safety Disclosures		84
Item 5. Other Information		84
Item 6. Exhibits		85

SIGNATURES		86

FORWARD-LOOKING STATEMENTS

This Quarterly Report on Form 10-Q, or the Quarterly Report, contains forward-looking statements. We intend such forward-looking statements to be covered by the safe harbor provisions for forward-looking statements contained in Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). All statements other than statements of historical facts contained in this Quarterly Report, including without limitation statements regarding our future results of operations and financial position including projected cash runway, requirement for additional funding, business strategy, including potential strategic partnership efforts, ability to recognize the benefits of and complete our obligations under the Transaction (as defined herein), including the Transaction Consideration (as defined herein), prospective products, the design, timing and results of our clinical studies and data readouts, product approvals, communications with, feedback from, or submissions to the FDA, research and development costs, timing and likelihood of success, our ability to continue as a going concern, our ability to maintain compliance with any applicable Nasdaq listing requirements, executive and director transition matters, plans and objectives of management for future operations and future results of anticipated products, or the timing of any of the foregoing, are forward-looking statements. These statements involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements.

In some cases, you can identify forward-looking statements by terms such as “may,” “will,” “should,” “expect,” “plan,” “anticipate,” “could,” “intend,” “target,” “project,” “contemplate,” “believe,” “estimate,” “predict,” “potential” or “continue” or the negative of these terms or other similar expressions. The forward-looking statements in this Quarterly Report are only predictions. We have based these forward-looking statements largely on our current expectations and projections about future events and financial trends that we believe may affect our business, financial condition and results of operations. These forward-looking statements speak only as of the date of this report and are subject to a number of important factors that could cause actual results to differ materially from those in the forward-looking statements, including the risks, uncertainties and assumptions described under the sections in this report titled “Summary Risk Factors,” “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and elsewhere in this Quarterly Report.

Moreover, we operate in an evolving environment. New risk factors and uncertainties may emerge from time to time, and it is not possible for management to predict all risk factors and uncertainties.

You should read this Quarterly Report and the documents that we reference in this Quarterly Report completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of our forward-looking statements by these cautionary statements. Except as required by applicable law, we do not plan to publicly update or revise any forward-looking statements contained herein, whether as a result of any new information, future events, changed circumstances or otherwise.

TRADEMARKS, SERVICE MARKS AND TRADENAMES

We have proprietary rights to trademarks used in this Quarterly Report, which are important to our business and many of which are registered under applicable intellectual property laws. Solely for convenience, the trademarks, service marks, logos and trade names referred to in this Quarterly Report are without the ® and ™ symbols, but such references are not intended to indicate, in any way, that we will not assert, to the fullest extent under applicable law, our rights to these trademarks, service marks and trade names. This Quarterly Report contains additional trademarks, service marks and trade names of others, which are the property of their respective owners. All trademarks, service marks and trade names appearing in this Quarterly Report are, to our knowledge, the property of their respective owners. We do not intend our use or display of other companies’ trademarks, service marks, copyrights or trade names to imply a relationship with, or endorsement or sponsorship of us by, any other companies.

SUMMARY RISK FACTORS

Our business is subject to numerous risks and uncertainties, including those described in Part II, Item 1A. “Risk Factors” in this Quarterly Report. You should carefully consider these risks and uncertainties when investing in our common stock. The principal risks and uncertainties affecting our business include the following:

•

We will need additional funding in order to advance development of our product candidates (including to complete the planned Phase 2 study of SER-155 in allo-HSCT) and commercialize our product candidates, if approved. If we are unable to raise capital or secure a partnership or other business development transaction, we could be required to implement further cost-reduction measures, reduce or delay our product development programs or potential future commercialization efforts, or pursue other alternatives, which could include seeking relief under the U.S. Bankruptcy Code or winding down our operations.

•

We have identified conditions and events that raise substantial doubt regarding our ability to continue as a going concern.

•

We are a clinical-stage company and have incurred significant losses since our inception. We expect to incur losses for the foreseeable future and may never achieve or maintain profitability.

•

The total amount of the Milestone Payments (as defined herein) we may receive from the Transaction (as defined herein), and the amounts payable or due under the Profit Sharing Payments (as defined herein), are subject to various risks and uncertainties.

•

We may not be able to realize the anticipated benefits of the Transaction (as defined herein), and we may face new challenges as a smaller, less diversified company.

•

Our limited operating history may make it difficult to evaluate the success of our business to date and to assess our future viability.

•

We are early in our development efforts of our product candidates and may not be successful in our efforts to use our reverse translational platform to build a pipeline of product candidates and develop additional marketable drugs.

•

Our product candidates are based on live biotherapeutics, which is a novel approach to therapeutic intervention.

•

Clinical drug development involves a risky, lengthy and expensive process, with an uncertain outcome. We may incur additional costs or experience delays in completing, or ultimately be unable to complete, the development and any potential future commercialization of our product candidates.

•

Delays or difficulties in the enrollment of patients in clinical trials, could result in our receipt of necessary regulatory approvals being delayed or prevented.

•

Disruptions at the FDA and other government agencies caused by funding shortages, government shutdowns, or staffing limitations could hinder their ability to hire, retain or deploy key leadership and other personnel, or otherwise prevent new or modified products from being developed, approved or commercialized in a timely manner or at all, which could negatively impact our business.

•

Current and future legislation or regulation may increase the difficulty and cost for us to obtain marketing approval of and commercialize our product candidates and may adversely affect the prices we may obtain.

•

If we are not able to obtain, or if there are delays in obtaining, required regulatory approvals, we or any collaborators will not be able to commercialize our product candidates or will not be able to do so as soon as anticipated, and our ability to generate revenue will be materially impaired. Additionally, failure to obtain marketing approval in international jurisdictions would prevent our product candidates from being marketed abroad.

•

We rely, and expect to continue to rely, on third parties to conduct our clinical trials, and those third parties may not perform satisfactorily, including failing to meet deadlines for the completion of such trials.

•

Even if any of our product candidates receive marketing approval, such product candidates may fail to achieve the degree of market acceptance by physicians, patients, hospitals, third-party payors and others in the medical community necessary for commercial success.

•

We face substantial competition, which may result in others discovering, developing or commercializing competing products before or more successfully than we do.

•

If we are unable to adequately protect our proprietary technology or obtain and maintain issued patents that are sufficient to protect our product candidates, others could compete against us more directly, which would have a material adverse impact on our business, results of operations, financial condition and prospects.

•

Our future success depends on our ability to manage our recent CEO transition, to retain key executives and to attract, retain and motivate qualified personnel.

•

Our recent reverse stock split may not result in the market price per share of our common stock to either exceed or remain in excess of the $1.00 minimum bid price as required by Nasdaq, or have any of its other anticipated impacts, and we may be unable to satisfy or maintain other Nasdaq continued listing rules.

PART I – FINANCIAL INFORMATION

Item 1. Condensed Consolidated Financial Statements (unaudited)

SERES THERAPEUTICS, INC.

CONDENSED CONSOLIDATED BALANCE SHEETS

(unaudited, in thousands, except share and per share data)


	September 30,			December 31,
	2025			2024
Assets
Current assets:
Cash and cash equivalents	$	47,638		$	30,793
Accounts receivable due from SPN - related party		426			2,068
Accounts receivable		351			—
Prepaid expenses and other current assets (1)		3,112			5,813
Total current assets		51,527			38,674
Property and equipment, net		8,578			11,534
Operating lease assets		74,669			80,903
Restricted cash		8,668			8,668
Other non-current assets		31			31
Total assets	$	143,473		$	139,810
Liabilities and Stockholders’ Equity
Current liabilities:
Accounts payable	$	1,677		$	4,079
Accrued expenses and other current liabilities		6,382			10,719
Accrued liabilities due to SPN - related party		4,450			17,750
Operating lease liabilities		9,920			8,674
Total current liabilities		22,429			41,222
Operating lease liabilities, net of current portion		75,333			82,966
Other long-term liabilities		2,014			1,838
Total liabilities		99,776			126,026
Commitments and contingencies (Note 9)
Stockholders’ equity (deficit):
Preferred stock, $0.001 par value; 10,000,000 shares authorized at September 30, 2025 and December 31, 2024; no shares issued and outstanding at September 30, 2025 and December 31, 2024		—			—
Common stock, $0.001 par value; 360,000,000 shares authorized at September 30, 2025 and December 31, 2024; 8,764,664 and 8,650,227 shares issued and outstanding at September 30, 2025 and December 31, 2024, respectively		9			9
Additional paid-in capital		1,000,756			991,874
Accumulated other comprehensive loss		—			—
Accumulated deficit		(957,068	)		(978,099	)
Total stockholders’ equity		43,697			13,784
Total liabilities and stockholders’ equity	$	143,473		$	139,810

[1] Includes $53 as of September 30, 2025 and $2,683 as of December 31, 2024 of unbilled receivable from SPN (related party) related to certain costs of the transition services performed by the Company. See Note 3, Discontinued Operations and TSA, for further details.

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

SERES THERAPEUTICS, INC.

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME

(unaudited, in thousands, except share and per share data)


	Three Months Ended September 30,						Nine Months Ended September 30,
	2025			2024			2025			2024
Revenue:
Grant revenue		351			—			351			—
Total revenue		351			—			351			—
Operating expenses:
Research and development expenses		12,616			16,460			37,376			51,759
General and administrative expenses		9,476			12,710			31,617			40,721
Manufacturing services		736			—			5,952			—
Total operating expenses		22,828			29,170			74,945			92,480
Loss from operations		(22,477	)		(29,170	)		(74,594	)		(92,480	)
Other income (expense):
Gain on sale of VOWST Business		27,222			—			79,588			—
Interest income		618			652			1,782			3,530
Other income (expense) (2)		2,841			(22,517	)		14,255			(21,184	)
Total other income (expense), net		30,681			(21,865	)		95,625			(17,654	)
Net income (loss) from continuing operations	$	8,204		$	(51,035	)	$	21,031		$	(110,134	)
Net income from discontinued operations, net of tax	$	—		$	139,811		$	—		$	125,907
Net income and comprehensive income	$	8,204		$	88,776		$	21,031		$	15,773
Net income (loss) from continuing operations per share attributable to common stockholders - basic	$	0.94		$	(6.69	)	$	2.41		$	(14.68	)
Net income from discontinued operations per share attributable to common stockholders - basic	$	—		$	18.32		$	—		$	16.78
Net income per share attributable to common stockholders - basic	$	0.94		$	11.63		$	2.41		$	2.10
Net income (loss) from continuing operations per share attributable to common stockholders - diluted	$	0.94		$	(6.69	)	$	2.40		$	(14.68	)
Net income from discontinued operations per share attributable to common stockholders - diluted	$	—		$	18.32		$	—		$	16.78
Net income per share attributable to common stockholders - diluted	$	0.94		$	11.63		$	2.40		$	2.10
Weighted average common shares outstanding - basic		8,758,692			7,632,242			8,735,418			7,504,763
Weighted average common shares outstanding - diluted		8,771,519			7,632,242			8,744,797			7,504,763

[2] Includes $2,028 and $11,827 for the three and nine months ended September 30, 2025 related to reimbursement received from SPN (related party) for transition services provided by the Company.

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

SERES THERAPEUTICS, INC.

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY (DEFICIT)

(unaudited, in thousands, except share data)


	Common Stock				Additional		Accumulated Other					Total
	Shares		Par Value		Paid-in Capital		Comprehensive Loss (Income)		Accumulated Deficit			Stockholders’ Equity
Balance at December 31, 2024		8,650,227	$	9	$	991,874	$	—	$	(978,099	)	$	13,784
Issuance of common stock upon vesting of RSUs and PSUs, net of tax withholdings		12,966		—		—		—		—			—
Issuance of common stock under ESPP		14,188		—		184		—		—			184
Issuance of common stock from at the market equity offering, net of issuance costs of $26		54,806		—		996		—		—			996
Stock-based compensation expense		—		—		2,819		—		—			2,819
Net income		—		—		—		—		32,682			32,682
Balance at March 31, 2025		8,732,187	$	9	$	995,873	$	—	$	(945,417	)	$	50,465
Issuance of common stock upon vesting of RSUs, net of tax withholdings		22,195		—		—		—		—			—
Stock-based compensation expense		—		—		2,340		—		—			2,340
Adjustment for fractional shares due to reverse stock split		100		—		—		—		—			—
Net loss		—		—		—		—		(19,855	)		(19,855	)
Balance at June 30, 2025		8,754,482	$	9	$	998,213	$	—	$	(965,272	)	$	32,950
Issuance of common stock upon exercise of stock options		782		—		15		—		—			15
Issuance of common stock upon vesting of RSUs, net of tax withholdings		5,749		—		—		—		—			—
Issuance of common stock under ESPP		3,651		—		46		—		—			46
Stock-based compensation expense		—		—		2,482		—		—			2,482
Net income		—		—		—		—		8,204			8,204
Balance at September 30, 2025		8,764,664	$	9	$	1,000,756	$	—	$	(957,068	)	$	43,697


	Common Stock				Additional		Accumulated Other					Total
	Shares		Par Value		Paid-in Capital		Comprehensive Loss (Income)		Accumulated Deficit			Stockholders’ (Deficit) Equity
Balance at December 31, 2023		6,752,073	$	7	$	933,372	$	—	$	(978,235	)	$	(44,856	)
Issuance of common stock upon vesting of RSUs and PSUs, net of tax withholdings		30,440		—		—		—		—			—
Issuance of common stock under ESPP		21,198		—		353		—		—			353
Issuance of common stock from at the market equity offering, net of issuance costs of $548		768,331		1		18,408		—		—			18,409
Stock-based compensation expense		—		—		6,489		—		—			6,489
Net loss		—		—		—		—		(40,133	)		(40,133	)
Balance at March 31, 2024		7,572,042	$	8	$	958,622	$	—	$	(1,018,368	)	$	(59,738	)
Issuance of common stock upon vesting of RSUs, net of tax withholdings		9,498		—		—		—		—			—
Stock-based compensation expense		—		—		5,534		—		—			5,534
Net loss		—		—		—		—		(32,870	)		(32,870	)
Balance at June 30, 2024		7,581,540	$	8	$	964,156	$	—	$	(1,051,238	)	$	(87,074	)
Issuance of common stock upon exercise of stock options		—		—		—		—		—			—
Issuance of common stock upon vesting of RSUs, net of tax withholdings		41,520		—		—		—		—			—
Issuance of common stock under ESPP		8,223		—		134		—		—			134
Issuance of common stock from Securities Purchase Agreement - related party		714,285		1		13,515		—		—			13,516
Issuance of common stock from at the market equity offering, net of issuance costs of $196		164,259		—		3,384		—		—			3,384
Stock-based compensation expense		—		—		5,183		—		—			5,183
Net income		—		—		—		—		88,776			88,776
Balance at September 30, 2024		8,509,827	$	9	$	986,372	$	—	$	(962,462	)	$	23,919

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

SERES THERAPEUTICS, INC.

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS

(unaudited, in thousands)


	Nine Months Ended September 30,
	2025			2024
Cash flows from operating activities:
Net income	$	21,031		$	15,773
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation expense		7,641			17,206
Depreciation and amortization expense		3,179			4,383
Non-cash operating lease cost		6,234			7,223
Gain on sale of VOWST Business, net of transaction costs		—			(146,707	)
Amortization of debt issuance costs		—			1,413
Loss associated with extinguishment of debt		—			23,351
Loss on disposal of fixed assets		—			293
Impairment of long-lived assets		—			3,267
Change in fair value of warrant liabilities		—			(546	)
Changes in operating assets and liabilities:
Accounts receivable due from SPN - related party		1,642			—
Accounts receivable		(351	)		—
Prepaid expenses and other current and other non-current assets		2,701			261
Collaboration receivable - related party		—			8,674
Inventories		—			(33,795	)
Deferred income - related party		—			(4,124	)
Accounts payable		(2,402	)		1,222
Accrued liabilities due to SPN - related party		(13,300	)		—
Operating lease liabilities		(6,387	)		(4,367	)
Accrued expenses and other current and long-term liabilities		(4,161	)		(3,254	)
Net cash provided by (used in) operating activities		15,827			(109,727	)
Cash flows from investing activities:
Purchases of property and equipment		(223	)		(290	)
Sales of restricted investments		—			1,401
Proceeds from sale of VOWST Business		—			141,272
Net cash (used in) provided by investing activities		(223	)		142,383
Cash flows from financing activities:
Proceeds from at the market equity offering, net of issuance costs		996			21,793
Proceeds from exercise of stock options		15			—
Proceeds from Securities Purchase Agreement - related party		—			13,516
Issuance of common stock under ESPP		230			487
Repayment of notes payable		—			(127,905	)
Net cash provided by (used in) financing activities		1,241			(92,109	)
Net increase (decrease) in cash, cash equivalents, and restricted cash		16,845			(59,453	)
Cash, cash equivalents and restricted cash at beginning of period		39,461			136,150
Cash, cash equivalents and restricted cash at end of period	$	56,306		$	76,697
Supplemental disclosure of cash flow information:
Cash paid for interest	$	—		$	10,858
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued expenses	$	—		$	13

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

SERES THERAPEUTICS, INC.

NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS

(Amounts in thousands, except share and per share data)

(Unaudited)

1. 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 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, which was sold to Nestlé Health Science (as defined below) in September 2024. The Company is progressing the development of SER-155, an investigational, oral, live biotherapeutic designed to decolonize gastrointestinal (“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”). The Company also continues to develop another proprietary live biotherapeutic composition, SER-147, designed to prevent bacterial bloodstream and spontaneous bacterial peritonitis infections in patients with metabolic disease, including chronic liver disease. SER-155 and the Company's other pipeline programs are designed to target multiple disease-relevant pathways and are manufactured from standard clonal cell banks via cultivation, rather than from the donor-sourced production process used for VOWST.

In the Company's placebo-controlled Phase 1b study of SER-155 in allo-HSCT, Cohort 2 results demonstrated that 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 hematopoietic stem cell transplantation (“HSCT”). SER-155 was generally well tolerated, with no observed treatment-related serious adverse events. In addition to allo-HSCT, the Company is exploring the potential of SER-155 and other cultivated live biotherapeutic candidates in other medically vulnerable patient populations, including autologous-HSCT patients, cancer patients with neutropenia, chimeric antigen receptors therapy recipients, individuals with chronic liver disease, solid organ transplant recipients, as well as patients in the intensive care unit and long-term acute care facilities.

In July 2025, the Company was awarded a grant from CARB-X (“Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator”) to support the development of an oral liquid formulation of SER-155 for medically vulnerable patient populations at risk of BSIs, including antimicrobial resistant infections, who cannot be dosed with oral capsules, such as intubated patients in the ICU. The CARB-X grant provides the Company with up to $3.6 million of funding for research, manufacture, and design of a Phase 1 clinical trial in ICU patients. The Company recognized $351 of grant revenue from CARB-X in the three months ended September 30, 2025.

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 microbiological capabilities and a strain library that spans broad biological and functional breadth to both identify specific microbes and microbial metabolites that are associated with disease and to design consortia of bacteria with specific pharmacological properties. 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 share 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 will reimburse 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. NESA has agreed to pay 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 will reimburse the Company for certain

costs of the transition services performed by the Company under the TSA, including labor. The Company will provide the manufacturing services until December 31, 2025 and other services for the duration specified in the schedule to the TSA for each service. Following the completion of PRMS manufacturing in the second quarter of 2025, manufacturing services primarily consist of costs incurred to ensure compliance of the facility and management of in-process inventories and samples. 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, upon NESA's request, the Company will transfer 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 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 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 have 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.

On September 23, 2025, the Company announced that it implemented cost reduction actions, including reducing its workforce by approximately 25% (including reductions that were effective in August 2025). During the three and nine months ended September 30, 2025, the Company incurred approximately $1,027 in restructuring costs, primarily related to severance costs. These costs are expected to be paid out in the fourth quarter of 2025.

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 condensed 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 September 30, 2025, the Company had an accumulated deficit of $957,068 and cash and cash equivalents of $47,638.

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 $74,594 for the nine months ended September 30, 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 condensed 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 condensed consolidated financial statements are issued. The accompanying condensed consolidated financial statements do not include any adjustments that may result from the outcome of this uncertainty.

Unaudited Interim Financial Information

The accompanying unaudited condensed consolidated financial statements as of September 30, 2025 and for the three and nine months ended September 30, 2025 and 2024 have been prepared by the Company, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These unaudited condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2024 included in the Company’s annual report on Form 10-K for the fiscal year ended December 31, 2024, which was filed with the SEC on March 13, 2025 (the “Annual Report”).

The unaudited condensed consolidated interim financial statements have been prepared on the same basis as the audited consolidated financial statements. The condensed consolidated balance sheet at December 31, 2024 was derived from audited annual financial statements, but does not contain all of the footnote disclosures from the annual financial statements. In the opinion of management, the accompanying unaudited interim condensed consolidated financial statements contain all adjustments which are necessary for a fair statement of the Company’s financial position, results of operations, and cash flows for the periods presented. Such adjustments are of a normal and recurring nature. The results of operations for the three and nine months ended September 30, 2025 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2025.

In late September 2024, the Company’s VOWST Business met all the conditions to be classified as held for sale and, because the Company considers the disposal of the VOWST Business to be a strategic shift that will have a major effect on its operations and

financial results, represented a discontinued operation. All assets and liabilities associated with the Company’s VOWST Business were therefore classified as assets and liabilities of discontinued operations in the Company's condensed consolidated balance sheets for the historical periods presented prior to the sale of the VOWST Business. Further, all historical operating results for the Company’s VOWST Business are reflected within discontinued operations in the condensed consolidated statements of operations for all periods presented. For additional information, see Note 3, Discontinued Operations and TSA.

The Company’s condensed consolidated financial statements include its accounts and the accounts of its wholly owned subsidiaries. All intercompany transactions have been eliminated in consolidation. The condensed consolidated financial statements have been prepared in conformity with U.S. GAAP.

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, Stockholders' Equity, for further information.

Reclassifications

Certain amounts in prior periods have been reclassified to reflect the impact of the discontinued operations treatment of the VOWST Business in order to conform to the current period presentation.

2. Summary of Significant Accounting Policies

The significant accounting policies and estimates used in preparation of the unaudited condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2024, and the notes thereto, which are included in the Annual Report. There have been no material changes to the Company’s significant accounting policies during the nine months ended September 30, 2025.

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 unaudited condensed consolidated financial statements and the reported amount of expenses during the reporting periods. In the unaudited condensed 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 those estimates.

Restricted Cash

The Company held restricted cash of $8,668 as of September 30, 2025 and December 31, 2024, which represents cash held for the benefit of the landlords for certain of the Company’s leases. The Company has classified the restricted cash as long-term on its condensed consolidated balance sheets as the terms of the underlying leases are greater than one year.

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


	September 30,		December 31,
	2025		2024
Cash and cash equivalents	$	47,638	$	30,793
Restricted cash, non-current		8,668		8,668
Total cash, cash equivalents and restricted cash	$	56,306	$	39,461

Recently Issued 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. The Company is currently evaluating the impact related to the adoption of ASU 2023-09 on its financial statement disclosures.

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.

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 were classified as assets and liabilities of discontinued operations in the condensed consolidated balance sheets for the historical periods presented prior to the sale of the VOWST Business and the results of operations from the VOWST Business were classified as discontinued operations in the condensed 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.

The Company has also entered into a Transition Services Agreement with NESA, an affiliate of SPN, in connection with the Transaction, through which the Company will provide 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 three and nine months ended September 30, 2025, the Company recognized $2,028 and $11,827, respectively, of TSA reimbursement income in other income in the Company’s condensed consolidated statements of operations and comprehensive income. For the three and nine months ended September 30, 2025, the Company has incurred $736 and $5,952, respectively, of expenses related to manufacturing services and $76 and $3,585, respectively, 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 three and nine months ended September 30, 2025, $1,756 and $13,743, respectively, has been billed to NESA related to transition services performed by the Company, and the Company received $2,212 and $90,385 from NESA during the periods, respectively, 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 condensed consolidated statements of operations and comprehensive income for the nine months ended September 30, 2025 as the gain was realizable. As of September 30, 2025, the Company has $426 in accounts receivable due from SPN - related party and $53 unbilled receivable included in prepaid expenses and other current asset in the Company’s condensed 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 condensed consolidated balance sheet as of September 30, 2025 and December 31, 2024 and consist of the following (in thousands):


	September 30,		December 31,
	2025		2024
Profit Sharing Payments	$	1,695	$	11,230
Royalties associated with the MSK Agreement		2,150		2,786
VOWST post-marketing safety surveillance study		222		771
80.1% of lease cost of Waltham facility		383		1,501
Employment-related costs for conveying employees		—		1,462
Total accrued liabilities due to SPN - related party	$	4,450	$	17,750

The contingent liabilities accrued on the Company's condensed consolidated balance sheet are remeasured at each reporting period 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 three and nine months ended September 30, 2025, the Company recognized a gain on sale of VOWST Business of $2,222 and $4,588, respectively, as a result of the change in accrued liabilities due to SPN - related party.

The Company has excluded from its condensed consolidated balance sheets the effects of 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 TSA and ii) 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 condensed consolidated statements of cash flows. There were no cash flows related to discontinued operations for the nine months ended September 30, 2025. For the nine months ended September 30, 2024, capital expenditures related to the VOWST Business were $112. Depreciation expense related to the VOWST Business for the same period was $989. Non-cash operating lease costs related to the VOWST Business for the nine months ended September 30, 2024 were $1,447, while the share based compensation expense for the same period was $1,884. Excluding the gain of $146,707 recognized on the sale of the VOWST Business presented in the condensed consolidated statements of cash flows for the nine months ended September 30, 2024, there were no other material operating or investing non-cash items related to the VOWST Business for either period presented.

4. Property and Equipment, Net

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


	September 30, 2025			December 31, 2024
Laboratory equipment	$	24,557		$	24,468
Computer equipment		4,058			3,924
Furniture and office equipment		4,523			4,523
Leasehold improvements		30,954			30,954
Construction in progress		861			861
		64,953			64,730
Less: Accumulated depreciation and amortization		(56,375	)		(53,196	)
	$	8,578		$	11,534

Depreciation and amortization expense was $1,044, $3,179, $1,404 and $4,383 for the three and nine months ended September 30, 2025 and 2024 respectively. The expense for the three and nine months ended September 30, 2024 includes amounts related to both continuing and discontinued operations. The Company did not dispose of any assets during the nine months ended September 30, 2025. During the nine months ended September 30, 2024, the Company disposed of certain assets with a cost basis of $594. In addition, during the nine months ended September 30, 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 September 30, 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 (in thousands):


	September 30, 2025		December 31, 2024
Clinical and development costs	$	282	$	422
Manufacturing and quality costs		143		478
Payroll and employee-related costs		4,444		7,656
Facility and other		1,513		2,163
	$	6,382	$	10,719

6. Leases

The Company leases real estate, primarily laboratory, office and manufacturing space. The Company’s leases have remaining terms ranging from approximately three to seven years. Certain leases include one or more options to renew, exercisable at the Company’s sole discretion, with renewal terms that can extend the lease from approximately one year to ten 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 income in the Company’s condensed consolidated statements of operations and comprehensive income (loss).

During the three months ended March 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 as a result of operational efficiencies implemented related to the production process 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 condensed consolidated statements of operations and comprehensive income (loss).

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


	September 30, 2025		December 31, 2024
Assets:
Operating lease assets	$	74,669	$	80,903

Liabilities:
Operating lease liabilities	$	9,920	$	8,674
Operating lease liabilities, net of current portion		75,333		82,966
Total operating lease liabilities	$	85,253	$	91,640

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


	Three Months Ended September 30,						Nine Months Ended September 30,
	2025			2024			2025			2024
Operating lease costs	$	4,781		$	5,701		$	14,399		$	17,177
Short-term lease costs		—			381			—			1,127
Variable lease costs		1,745			1,801			4,708			5,729
Sublease income		(814	)		(814	)		(2,446	)		(1,884	)
Total lease costs	$	5,712		$	7,069		$	16,661		$	22,149

During the three and nine months ended September 30, 2025 and 2024, the Company made cash payments for operating leases of

$4,837, $14,552, $5,364 and $14,321, respectively. The lease cost and lease payment amounts above include amounts related to discontinued operations for the three and nine months ended September 30, 2024.

As of September 30, 2025, future payments of operating lease liabilities are as follows (in thousands):


	As of September 30, 2025
2025 (remaining 3 months)	$	4,888
2026		19,983
2027		20,582
2028		20,863
2029		20,132
2030 and thereafter		36,850
Total future minimum lease payments	$	123,298
Less: interest		(38,045	)
Present value of operating lease liabilities	$	85,253

As of September 30, 2025, the weighted average remaining lease term was 6.29 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 13%. As of September 30, 2024, the weighted average remaining lease term was 7.21 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 13%.

7. Common Stock and Stock-Based Awards

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.

Additionally, at the 2025 Annual Meeting, stockholders approved the Seres Therapeutics, Inc. 2025 Incentive Award Plan (the “2025 Plan”) as an amendment and restatement of the Seres Therapeutics, Inc. 2015 Incentive Award Plan (the “2015 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.

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 May 21, 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 nine months ended September 30, 2025, the Company sold 54,806 shares of common stock under the Sales Agreement, at an average price of approximately $18.60 per share, raising aggregate net proceeds of approximately $996 after deducting an aggregate commission of approximately 3% and other issuance costs. During the three and nine months ended September 30, 2024, the Company sold

164,259 and 932,590 shares of common stock under the Sales Agreement, respectively, at an average price of approximately $21.80 and $24.17 per share, raising aggregate net proceeds of approximately $3,384 and $21,793 after deducting an aggregate commission of approximately 3% and other issuance costs.

Between September 30, 2025 and October 31, 2025, the Company sold 268,081 shares of common stock under the Sales Agreement, at an average price of approximately $19.48 per share, raising aggregate net proceeds of approximately $5,091 after deducting an aggregate commission of approximately 3% and other issuance costs.

Stock Options

The following table summarizes the Company’s stock option activity since December 31, 2024:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2024		886,123		$	129.29		6.59	$	87
Granted		546,805		$	15.14
Exercised		(782	)	$	18.99
Forfeited		(243,414	)	$	126.37
Outstanding as of September 30, 2025		1,188,732		$	66.41		7.29	$	2,288
Vested or expected to vest as of September 30, 2025		1,188,732		$	66.41		7.29	$	2,288
Options exercisable as of September 30, 2025		499,771		$	131.18		5.17	$	202

The weighted average grant date fair value of stock options granted during the three and nine months ended September 30, 2025 and 2024 was $10.34, $13.30, $17.59 and $18.58 per share, respectively.

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 the three and nine months ended September 30, 2025 and 2024, the Company recognized $190, $451, $207, and $633, respectively, 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 following table summarizes the Company’s RSU and PSU activity since December 31, 2024:


	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2024		81,459		$	55.36
Granted		79,846		$	18.29
Vested		(52,160	)	$	41.84
Forfeited		(8,321	)	$	64.48
Unvested restricted stock units as of September 30, 2025		100,824		$	32.24

During the three and nine months ended September 30, 2025 and 2024, the Company granted 68,596, 79,846, 0, and 64,316 RSUs, respectively. During the three and nine months ended September 30, 2025 and 2024, the Company did not grant any PSUs. RSUs generally vest over four years, with 25% vesting after one 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 three months ended March 31, 2023, the Company granted PSUs to employees for the purchase of 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 $194 and $721 in compensation expense during the three and nine months ended September 30, 2024, with respect to these PSUs. The remaining compensation expense associated with these PSUs was fully recognized as of December 31, 2024.

In September 2025, the Company issued retention awards to employees of the Company in the form of RSUs for the purchase of 68,596 shares of common stock with a grant date fair value of $18.93 per share. The retention RSUs will become 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 will be recognized ratably over the vesting period. For the three and nine months ended September 30, 2025, the Company recognized $104 in compensation expense with respect to the retention RSUs.

Stock-based Compensation Expense

The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive income (loss) (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2025		2024		2025		2024
Research and development expenses	$	1,076	$	2,955	$	3,417	$	9,400
General and administrative expenses		1,406		2,228		4,224		7,806
	$	2,482	$	5,183	$	7,641	$	17,206

For the three and nine months ended September 30, 2024, the table above includes stock-based compensation amounts related to discontinued operations.

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):


	Three Months Ended September 30,					Nine Months Ended September 30,
	2025		2024			2025		2024
Basic Earnings Per Share:
Numerator:
Net income (loss) from continuing operations attributable to common stockholders	$	8,204	$	(51,035	)	$	21,031	$	(110,134	)
Net income from discontinuing operations attributable to common stockholders	$	—	$	139,811		$	—	$	125,907
Net income attributable to common stockholders - basic	$	8,204	$	88,776		$	21,031	$	15,773

Denominator:
Weighted-average shares outstanding - basic		8,758,692		7,632,242			8,735,418		7,504,763
Net income (loss) from continuing operations per share attributable to common stockholders - basic	$	0.94	$	(6.69	)	$	2.41	$	(14.68	)
Net income from discontinued operations per share attributable to common stockholders - basic	$	—	$	18.32		$	—	$	16.78
Net income per share attributable to common stockholders - basic	$	0.94	$	11.63		$	2.41	$	2.10

Diluted Earnings Per Share:
Numerator:
Net income (loss) from continuing operations attributable to common stockholders	$	8,204	$	(51,035	)	$	21,031	$	(110,134	)
Net income from discontinuing operations attributable to common stockholders	$	—	$	139,811		$	—	$	125,907
Net income attributable to common stockholders - diluted	$	8,204	$	88,776		$	21,031	$	15,773

Denominator:
Weighted-average shares outstanding - basic		8,758,692		7,632,242			8,735,418		7,504,763

Dilutive impact from:
Stock options to purchase common stock		2,139		—			—		—
Unvested restricted stock units		8,990		—			9,377		—
Shares issuable under employee stock purchase plan		1,698		—			2		—
Weighted-average shares outstanding - diluted		8,771,519		7,632,242			8,744,797		7,504,763
Net income (loss) per share applicable to common stockholders - diluted	$	0.94	$	(6.69	)	$	2.40	$	(14.68	)
Net income from discontinuing operations attributable to common stockholders - diluted	$	—	$	18.32		$	—	$	16.78
Net income attributable to common stockholders - diluted	$	0.94	$	11.63		$	2.40	$	2.10

Anti-dilutive potential common stock equivalents excluded from the calculation of net income (loss) per share:
Stock options to purchase common stock		1,188,732		956,015			1,188,732		956,015
Unvested restricted stock units		100,824		137,642			100,824		137,642
Shares issuable under employee stock purchase plan		1,256		5,002			423		1,679
Warrants to purchase common stock		32,379		32,379			32,379		32,379

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 three and nine months ended September 30, 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 three and nine months ended September 30, 2024 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 three and nine months ended September 30, 2024.

9. Commitments and Contingencies

Leases

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

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of September 30, 2025 or December 31, 2024.

Legal Contingencies

The Company accrues a liability for legal contingencies when it believes that it is both probable that a liability has been incurred and that the Company can reasonably estimate the amount of the loss. The Company reviews these accruals and adjusts them to reflect ongoing negotiations, settlements, rulings, advice of legal counsel and other relevant information. To the extent new information is obtained and the views on the probable outcomes of claims, suits, assessments, investigations or legal proceedings change, changes in the Company’s accrued liabilities would be recorded in the period in which such determination is made.

In addition, in accordance with the relevant authoritative guidance, for any matters in which the likelihood of material loss is at least reasonably possible, the Company will provide disclosure of the possible loss or range of loss. If a reasonable estimate cannot be made, however, the Company will provide disclosure to that effect. The Company expenses legal costs as they are incurred.

The Company did not accrue any liabilities related to legal contingencies in its consolidated financial statements as of September 30, 2025 or December 31, 2024.

10. Income taxes

The Company did not provide for any income taxes in its condensed consolidated statement of operations and comprehensive income for the three and nine months ended September 30, 2025 and 2024. While the Company has net income for book purposes for the nine months ended September 30, 2025, the Company is projecting tax losses for the full year ending December 31, 2025, for which it is more likely than not that the Company will not realize a benefit. Based on its evaluation of the positive and negative evidence bearing upon its ability to realize its deferred tax assets, the Company determined that it is more likely than not that it will not realize such benefits. Accordingly, the Company has recorded a full valuation allowance against its deferred tax assets as of September 30, 2025 and December 31, 2024, and has not recorded any income taxes for the three and nine months ended September 30, 2025 and 2024. Management reevaluates the positive and negative evidence at each reporting period.

On July 4, 2025, the One Big Beautiful Bill Act (“OBBBA”), which includes a broad range of tax reform provisions, was signed into law in the United States. The impact of the OBBBA is not expected to be material to the Company’s consolidated balance sheet or consolidated statements of operations and comprehensive income for the year ended December 31, 2025.

11. Related Party Transactions

As described in Note 1, Nature of the Business and Basis of Presentation and Note 3, Discontinued Operations and TSA, in September 2024, the Company sold 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 VOWST, to SPN, and SPN assumed certain liabilities from the Company. As consideration for the Transaction, the Company received an upfront cash payment of $139,788, which 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 fees due under the Bacthera Manufacturing Agreement; plus a prepayment of the $60,000 milestone payment tied to the achievement of worldwide annual net sales of VOWST of $150,000; plus an equity investment of $15,000 based on the Securities Purchase Agreement pursuant to which SPN purchased 714,285 shares of common stock at a purchase price of $21.00 per share.

As of September 30, 2025, there was $4,450 included in Accrued Liabilities due to SPN - related party on the Company’s condensed consolidated balance sheet, which represents amounts due to SPN pursuant to the Purchase Agreement, which are further described in Note 3, Discontinued Operations and TSA. During the three and nine months ended September 30, 2025, the Company paid $6,284 and $7,593 to SPN related to the Purchase Agreement during the periods, respectively.

As described in Note 3, Discontinued Operations and TSA, the Company entered into the TSA with NESA, an affiliate of SPN, in connection with the Transaction, through which the Company will provide 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 three and nine months ended September 30, 2025, the Company recognized $2,028 and $11,827, respectively, of TSA reimbursement income in other income in the Company’s condensed consolidated statements of operations and comprehensive income (loss). For the three and nine months ended September 30, 2025, the Company has incurred $736 and $5,952, respectively, of expenses related to manufacturing services and $76 and $3,585, respectively, of TSA labor and passthrough expenses to support the transition services, including finance and accounting, information technology, human resources, operations, and other services.

During the three and nine months ended September 30, 2025, $1,756 and $13,743, respectively, has been billed to NESA related to transition services performed by the Company, and the Company received payments of $2,212 and $90,385, respectively, related to transition services performed, which includes 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. As of September 30, 2025, the Company has $426 in accounts receivable due from SPN - related party and $53 unbilled receivable included in prepaid expenses and other current assets in the Company’s condensed consolidated balance sheets.

12. Segment Reporting

The Company’s co-Chief Executive Officers, who are the Chief Operating Decision Makers (“CODMs”), manage and allocate resources to the operations of the Company on a total company basis by assessing the overall level of resources available and how to best deploy these resources across functions and research and development projects that are in line with the Company’s long-term company-wide strategic goals. The CODMs use the Company’s consolidated net income (loss) to monitor actual results versus the budget in assessing segment performance and the allocation of resources. The measure of segment assets is reported on the consolidated balance sheets as total assets.

The Company's reportable segment net income (loss) for the three and nine months ended September 30, 2025 and 2024, consisted of the following (in thousands):

Seres Therapeutics, Inc. 10-Q