X0202 SCHEDULE 13G 0001727492 XXXXXXXX LIVE Common Stock, par value $0.0001 per share 03/31/2026 0001829802 Sensei Biotherapeutics, Inc. 81728A207 1405 RESEARCH BLVD, SUITE 125 ROCKVILLE MD 20850 Rule 13d-1(b) Caligan Partners LP DE 0.00 126002.00 0.00 126002.00 126002.00 N 9.40 IA PN In addition to the shares of the Issuer's common stock (the "Common Stock") provided for in rows (6), (8) and (9), the Reporting Persons hold Series B Non-Voting Convertible Preferred Stock (the "Preferred Stock") that, when convertible, may be converted into 361,010 shares of Common Stock. The Preferred Stock will be convertible at such time as, and otherwise in accordance with the terms, provided in the Certificate of Designation governing such Preferred Stock. David Johnson X1 0.00 126002.00 0.00 126002.00 126002.00 N 9.40 HC IN In addition to the shares of the Issuer's common stock (the "Common Stock") provided for in rows (6), (8) and (9), the Reporting Persons hold Series B Non-Voting Convertible Preferred Stock (the "Preferred Stock") that, when convertible, may be converted into 361,010 shares of Common Stock. The Preferred Stock will be convertible at such time as, and otherwise in accordance with the terms, provided in the Certificate of Designation governing such Preferred Stock. Sensei Biotherapeutics, Inc. 1405 Research Boulevard, Suite 125, Rockville, Maryland 20850. This statement is filed by: (i) Caligan Partners LP, a Delaware limited partnership ("Caligan"), which serves indirectly as the investment manager to Caligan Partners Master Fund LP, a Cayman Islands limited partnership (the "Caligan Fund"), and managed accounts (the "Caligan Accounts"), with respect to the shares of common stock, par value $0.0001 per share ("Common Stock"), of Sensei Biotherapeutics, Inc., a Delaware corporation (the "Company"), held, and issuable upon exercise of warrants held, by the Caligan Fund and Caligan Accounts; and (ii) David Johnson, the Managing Partner of Caligan and Managing Member of Caligan Partners GP LLC, the general partner of Caligan ("Mr. Johnson"), with respect to the shares of Common Stock held, and issuable upon exercise of warrants held, by the Caligan Fund and Caligan Accounts. Each of the foregoing is referred to as a "Reporting Person" and collectively as the "Reporting Persons." The principal business address of each of the Reporting Persons is 780 Third Avenue, 30th Floor, New York, NY 10017. Caligan is a Delaware limited partnership. Mr. Johnson is a United States citizen. N IA HC The information required by Item 4(a) is set forth in Row 9 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The percentages set forth in this Schedule 13G are calculated based upon an aggregate of 1,340,281 shares of Common Stock outstanding as of March 23, 2026, as reported in the Company's Annual Report on Form 10-K for the fiscal year ended December 31, 2025, filed with the Securities and Exchange Commission on March 30, 2026. 9.40% The information required by Item 4(c)(i) is set forth in Row 5 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The information required by Item 4(c)(ii) is set forth in Row 6 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The information required by Item 4(c)(iii) is set forth in Row 7 of the cover page for each of the Reporting Persons and is incorporated herein by reference. The information required by Item 4(c)(iv) is set forth in Row 8 of the cover page for each of the Reporting Persons and is incorporated herein by reference. Y N See Item 2(a). Y Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11. Exhibit 99.1: Joint Filing Agreement Caligan Partners LP /s/ David Johnson 05/15/2026 David Johnson /s/ David Johnson 05/15/2026