SNSE Sensei Biotherapeutics Inc

Exhibit 3.1

CERTIFICATE OF AMENDMENT

TO

AMENDED AND RESTATED CERTIFICATE OF INCORPORATION

OF

SENSEI BIOTHERAPEUTICS, INC.

Sensei Biotherapeutics, Inc. (the “Company”), a corporation organized and existing under and by virtue of the General Corporation Law of the State of Delaware (the “DGCL”), does hereby certify that:

FIRST: The name of this corporation is Sensei Biotherapeutics, Inc., and the date on which the Certificate of Incorporation of this corporation was originally filed with the Secretary of State of the State of Delaware on December 1, 2017, under the name PPI Holdings, Inc. The Certificate of Incorporation was amended and restated by an Amended and Restated Certificate of Incorporation on December 29, 2020 and on February 8, 2021.

SECOND: The Board of Directors of the Company (the “Board”), acting in accordance with the provisions of Sections 141 and 242 of the DGCL, adopted resolutions amending its Certificate of Incorporation (the “Certificate of Incorporation”), as follows:

Effective as of the effective time of 5:00 p.m., Eastern Time, on June 16, 2025 (the “Effective Time”), each twenty (20) shares of the Company’s Common Stock, par value $0.0001 per share, issued and outstanding immediately prior to the Effective Time shall, automatically and without any action on the part of the Company or the respective holders thereof, be combined into one (1) share of Common Stock without increasing or decreasing the par value of each share of Common Stock (the “Reverse Split”); provided, however, no fractional shares of Common Stock shall be issued as a result of the Reverse Split and, in lieu thereof, upon receipt after the Effective Time by the exchange agent selected by the Company of a properly completed and duly executed transmittal letter and, where shares are held in certificated form, the surrender of the stock certificate(s) formerly representing shares of pre-Reverse Split Common Stock, any stockholder who would otherwise be entitled to a fractional share of post-Reverse Split Common Stock as a result of the Reverse Split, following the Effective Time (after taking into account all fractional shares of post-Reverse Split Common Stock otherwise issuable to such stockholder), shall be entitled to receive a cash payment (without interest) equal to the fractional share of post-Reverse Split Common Stock to which such stockholder would otherwise be entitled multiplied by the average of the closing sales prices of a share of the Company’s Common Stock (as adjusted to give effect to the Reverse Split) on The Nasdaq Stock Market for each of the five (5) consecutive trading days immediately preceding the date this Certificate of Amendment is filed with the Secretary of State of the State of Delaware. Each stock certificate that, immediately prior to the Effective Time, represented shares of pre-Reverse Split Common Stock shall, from and after the Effective Time, automatically and without any action on the part of the Company or the respective holders thereof, represent that number of whole shares of post-Reverse Split Common Stock into which the shares of pre-Reverse Split Common Stock represented by such certificate shall have been combined (as well as the right to receive cash in lieu of any fractional shares of post-Reverse Split Common Stock as set forth above; provided, however, that each holder of record of a certificate that represented shares of pre-Reverse Split Common Stock shall receive, upon surrender of such certificate, a new certificate representing the number of whole shares of post-Reverse Split Common Stock into which the shares of pre-Reverse Split Common Stock represented by such certificate shall have been combined pursuant to the Reverse Split, as well as any cash in lieu of fractional shares of post-Reverse Split Common Stock to which such holder may be entitled as set forth above. The Reverse Split shall be effected on a record holder-by-record holder basis, such that any fractional shares of post-Reverse Split Common Stock resulting from the Reverse Split and held by a single record holder shall be aggregated.

Section A of Article IV of the Certificate of Incorporation is amended and restated to read in its entirety as follows:

“A. The Company is authorized to issue two classes of stock to be designated, respectively, “Common Stock” and “Preferred Stock.” The total number of shares of all classes of capital stock which the Company shall have authority to issue is 22,500,000 shares, of which 12,500,000 shall be Common Stock (the “Common Stock”), each share having a par value of one-hundredth of one cent ($0.0001), and 10,000,000 shall be Preferred Stock (the “Preferred Stock”), each share having a par value of one-hundredth of one cent ($0.0001).”

THIRD: The foregoing amendment to the Certificate of Incorporation was duly approved by the Board.

FOURTH: Thereafter, pursuant to a resolution of the Board, this Certificate of Amendment was submitted to the stockholders of the Company for their approval, and was duly adopted in accordance with the provisions of Section 242 of the DGCL.

FIFTH: This amendment to the Certificate of Incorporation shall be effective on and as of as of the effective time of 5:00 p.m., Eastern Time, on June 16, 2025.

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IN WITNESS WHEREOF, Sensei Biotherapeutics, Inc. has caused this Certificate of Amendment to be executed by its Chief Executive Officer as of June 12, 2025.