of this Current Report, including Exhibit 99.1 attached hereto, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Entry into a Material Definitive Agreement. Lease Amendment and Termination Agreement On July 31, 2026 (the “Execution Date”), Seres Therapeutics, Inc. (the “Company”) entered into the Third Amendment to Lease and Termination Agreement (the “Termination Agreement”) with BMR-Sidney Research Campus LLC, a Delaware limited liability company (the “Sidney Street Landlord”), the purpose of which is to effect an early termination of one of the Company’s leases, reducing the Company’s ongoing annual…

Termination of a Material Definitive Agreement. The information set forth under the heading “Lease Amendment and Termination Agreement” in

The excerpt does not provide specific details about a management change.

Other Events. On July 8, 2026, the Company announced top-line results from an IST evaluating SER-155 in patients with irEC. The study (NCT06801067), conducted at MSK, by Principal Investigator David Faleck, M.D., Director of Inflammatory and Immune-Related Bowel Diseases, evaluated SER-155 in 15 patients with moderate-to-severe (Grade 2- 3) irEC, which affects approximately 25% of all immune checkpoint inhibitor (ICI) therapy recipients in the US. Clinical guidelines for these patients stipul…

Entry into a Material Definitive Agreement. Amendment of Asset Purchase Agreement On June 2, 2026, Seres Therapeutics, Inc. (the “Company”) entered into Amendment No. 1 (the “APA Amendment”) to the Asset Purchase Agreement, dated as of August 5, 2024 (as previously amended by that certain Letter Agreement, dated September 30, 2024 and that certain Letter Agreement, dated December 31, 2024, the “Purchase Agreement”), by and between the Company and Société des Produits Nestlé S.A., a société an…

Director — Hans-Juergen Woerle, M.D., Ph.D.: Dr. Woerle resigned from his position as a member of the board of directors and on the committees he serves.

of this Current Report, including Exhibit 99.1 attached hereto, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Results of Operations and Financial Condition. On March 12, 2026, Seres Therapeutics, Inc. (the “Company”) announced its financial results for the quarter and year ended December 31, 2025 and provided operational updates. The full text of the press release issued in connection with the announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K (the “Current Report”).

Executive Chair of the Board and Interim Chief Executive Officer (Richard N. Kender), President (Matthew Henn, Ph.D.), Executive Vice President, Chief Operating Officer (Kelly Brady) — Richard N. Kender, Matthew Henn, Ph.D., Kelly Brady: The company appointed internal executives to new senior roles.

Results of Operations and Financial Condition. On November 5, 2025, Seres Therapeutics, Inc. (the “Company”) announced its financial results for the quarter ended September 30, 2025 and provided operational updates. The full text of the press release issued in connection with the announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K (the “Current Report”).

Other Events. On September 23, 2025, Seres Therapeutics, Inc. (the “Company”) announced actions to reduce operating costs in order to extend its cash runway to provide additional opportunities to advance its strategic priorities. In this announcement, the Company reported that it was reducing its workforce by approximately 25% (including reductions that were effective in August 2025), and the workforce reduction is expected to result in cash charges of approximately $1.0 to $1.4 million, prim…

Results of Operations and Financial Condition. On August 6, 2025, Seres Therapeutics, Inc. (the “Company”) announced its financial results for the quarter ended June 30, 2025 and provided operational updates. The full text of the press release issued in connection with the announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K (the “Current Report”).

Results of Operations and Financial Condition. On May 7, 2025, Seres Therapeutics, Inc. (the “Company”) announced its financial results for the quarter ended March 31, 2025 and provided operational updates. The full text of the press release issued in connection with the announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K (the “Current Report”).

The excerpt does not provide specific details about a management change.

Other Events. On April 10, 2025, at the Annual Meeting, the stockholders of the Company approved amendments to the Company’s Certificate of Incorporation to effect a reverse stock split of all outstanding shares of the Company’s common stock, at a ratio ranging from any whole number between 1-for-5 and 1-for-50, with the exact ratio as determined by the Board in its discretion, subject to the Board’s authority to abandon such amendments. On April 10, 2025, the Board approved a reverse stock s…

Results of Operations and Financial Condition. On March 13, 2025, Seres Therapeutics, Inc. (the “Company”) announced its financial results for the quarter and year ended December 31, 2024 and provided operational updates. The full text of the press release issued in connection with the announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K (the “Current Report”).

Executive Vice President and Chief Medical Officer — Lisa von Moltke, M.D.: Dr. Lisa von Moltke resigned to accept a new position at another company.

Class III director — Hans-Juergen Woerle, M.D.: Dr. Woerle was appointed as a new Class III director and will serve on the Science and Clinical Development Committee.

Other Events. As noted above, on January 9, 2025, the Company announced translational biomarker results from exploratory endpoints in its SER-155 Phase 1b placebo-controlled study in patients undergoing allogeneic hematopoietic stem cell transplantation (“allo-HSCT”). Following SER-155 administration, there was a statistically significant decrease in fecal albumin, an established biomarker of epithelial barrier integrity, and a positive impact on biomarkers of systemic inflammation and immune…

of this Current Report, including Exhibit 99.1, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly provided by specific reference in such a filing. The Company undertakes no obligation to update, supplement or ame…

Regulation FD Disclosure. On November 13, 2024, the Company posted an updated corporate presentation in the “Investors and News” portion of its website at www.serestherapeutics.com. A copy of the slide presentation is attached as Exhibit 99.2 to this Current Report and incorporated herein by reference. The information in Items 2.02 and 7.01 of this Current Report, including Exhibits 99.1 and 99.2 attached hereto, shall not be deemed “filed” for purposes of Section 18 of the Securities Exchang…

Results of Operations and Financial Condition. On November 13, 2024, Seres Therapeutics, Inc. (the “Company”) announced its financial results for the quarter ended September 30, 2024 and provided operational updates. The full text of the press release issued in connection with the announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K (the “Current Report”).

Notice of Delisting or Failure to Satisfy a Continued Listing Rule or Standard; Transfer of Listing. On November 7, 2024, the Company received a letter from the Listing Qualifications Department of The Nasdaq Stock Market LLC (“Nasdaq”) notifying the Company that, for the last 30 consecutive business days, the bid price for the Company’s common stock, par value $0.001 per share (the “Common Stock”), had closed below the $1.00 per share minimum bid price requirement for continued inclusion on…

and shall be deemed to be furnished, and not filed: Exhibit No. Description 99.1 Seres Therapeutics, Inc. SER-155 Phase 1b Cohort 2 Study Results Slide Presentation as of September 2024 99.2 Seres Therapeutics, Inc. SER-155 Phase 1b Cohort 2 Study Results Press Release issued September 12, 2024 99.3 Seres Therapeutics, Inc. Corporate Presentation as of September 2024 104 Cover Page Interactive Data File - the cover page XBRL tags are embedded within the Inline XBRL document. Important Additio…