On April 21, 2025, Seres Therapeutics, Inc. (the “Company”) filed a Certificate of Amendment to its Restated Certificate of Incorporation (the “Charter Amendment”) with the Secretary of State of the State of Delaware to effect a 1-for-20 reverse stock split (the “Reverse Stock Split”) of the Company’s common stock, par value $0.001 per share (the “Common Stock”), effective April 21, 2025 at 5:00 p.m., Eastern Time (the “Effective Time”). The Company’s Common Stock began trading on a split-adjusted basis on The Nasdaq Global Select Market at the commencement of trading on April 22, 2025 under the Company’s existing trading symbol “MCRB”. The new CUSIP number for the Common Stock following the Reverse Stock Split is 81750R 201.

As previously reported, at its Annual Meeting of Stockholders held on April 10, 2025, and upon the recommendation of the Company’s Board of Directors (the “Board”), the Company’s stockholders approved amendments to the Restated Certificate of Incorporation to effect a reverse stock split of the Common Stock at a ratio ranging from any whole number between 1-for-5 and 1-for-50, as determined by the Board in its discretion. On April 10, 2025, the Board approved a final Reverse Stock Split ratio of 1-for-20 and abandoned all other reverse stock split amendments at different ratios.

As a result of the Reverse Stock Split, at the Effective Time, every 20 shares of the Company’s issued and outstanding shares of Common Stock immediately prior to the Effective Time, were automatically converted, without any action on the part of the holder thereof, into one validly issued, fully-paid and non-assessable share of Common Stock, subject to the treatment of fractional shares as described below. The Charter Amendment did not affect the number of authorized shares of Common Stock or the par value of each share of Common Stock.

No fractional shares of Common Stock will be issued as a result of the Reverse Stock Split. Holders who otherwise would be entitled to receive a fractional share of Common Stock in connection with the Reverse Stock Split will receive a cash payment in lieu thereof.

The foregoing description is qualified in its entirety by the full text of the Charter Amendment, a copy of which is filed as Exhibit 3.1 to this Current Report on Form 8-K (this “Current Report”) and is incorporated herein by reference.

Forward-Looking Statements

This Current Report contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this Current Report that do not relate to matters of historical fact should be considered forward-looking statements, including without limitation statements regarding the trading of the Common Stock on a split-adjusted basis and the impact of the Reverse Stock Split, including any adjustments from the treatment of fractional shares; and other statements that are not historical fact. These forward-looking statements are based on management’s current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause the Company’s actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the important factors discussed under the caption “Risk Factors” in the Company’s Annual Report on Form 10-K filed with the SEC on March 13, 2025, and the Company’s other reports filed with the Securities and Exchange Commission could cause actual results to differ materially from those indicated by the forward-looking statements made in this Current Report. Any such forward-looking statements represent management’s estimates as of the date of this Current Report. While we may elect to update such forward-looking statements at some point in the future, we disclaim any obligation to do so, even if subsequent events cause the Company’s views to change. These forward-looking statements should not be relied upon as representing the Company’s views as of any date subsequent to the date of this Current Report.