Seres Therapeutics announces plans for irEC study

Item 2.02.

Results of Operations and Financial Condition.

On November 4, 2026, Seres Therapeutics, Inc. (the "Company") announced its financial results for the quarterly period ended September 30, 2026 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-K¹ (the "Current Report").

Item 7.01

Regulation FD Disclosure.

On November 4, 2026, the Company posted an updated corporate presentation (the "Corporate Presentation") to its website². A copy of the Corporate Presentation is furnished 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 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.

Item 9.01.

Financial Statements and Exhibits.

(d) Exhibits

Exhibit

No.

Description

99.1

Seres Therapeutics, Inc. Press Release issued November 4, 2026

99.2

Seres Therapeutics, Inc. Corporate Presentation dated November 4, 2026

104

Cover Page Interactive Data File (embedded within the Inline XBRL document)

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

SERES THERAPEUTICS, INC.

Date: November 4, 2026

By:

/s/ Thomas J. DesRosier

Name:

Thomas J. DesRosier

Title:

Executive Vice President and Chief Legal Officer

SERES THERAPEUTICS REPORTS THIRD QUARTER 2026 FINANCIAL RESULTS AND ANNOUNCES PLANS FOR ADVANCING DEVELOPMENT OF SER-155 TO PREVENT IMMUNE CHECKPOINT INHIBITOR-RELATED ENTEROCOLITIS (irEC)

Prevention approach aims to keep patients on immune checkpoint inhibitor (ICI) therapy and avoid immunosuppressive irEC treatments, representing an additional broad therapeutic opportunity for SER-155

Seres expects to submit plans for the next irEC study design to the FDA in Q1 2027³

Study builds on encouraging investigator-sponsored trial (IST) results, in which 12 of 15 participants (80%) with moderate-to-severe irEC achieved an immunosuppressive-free clinical response of diarrhea following treatment with SER-155⁵

CAMBRIDGE, Mass., November 4, 2026 — Seres Therapeutics, Inc. (Nasdaq: MCRB), (Seres or the Company), a leading live biotherapeutics company, today reported third quarter 2026 financial results and announced it is progressing plans for a next study evaluating SER-155 for the prevention of immune checkpoint inhibitor-related enterocolitis (irEC) in patients initiating immune checkpoint inhibitor (ICI) cancer therapy⁴, which is expected to include a dose optimization component. The Company anticipates submitting the study design to the FDA in the first quarter of 2027.⁴

The plan⁴