X0407 4 2023-07-10 0 0001829802 Sensei Biotherapeutics, Inc. SNSE 0001843594 Peyer James C/O SENSEI BIOTHERAPEUTICS, INC. 451 D STREET, SUITE 710 BOSTON MA 02210 1 0 1 0 0 Common Stock 2023-07-10 4 A 0 4466 0.00 A 5240422 I See footnote Stock Option (Right to Buy) 1.22 2023-07-10 4 A 0 14550 0.00 A 2033-07-09 Common Stock 14550 14550 I See footnote These shares represent restricted stock units (the "RSUs"). Each RSU represents a contingent right to receive one share of the common stock of the Issuer. The shares underlying the RSUs vest in full on the first anniversary of the date of grant, or July 10, 2024, subject to the Reporting Person's continuous service with the Issuer through such vesting date. These shares are held by Cambrian Biopharma Inc, a Delaware corporation ("Cambrian"). The Reporting Person is the Chief Executive Officer of Cambrian and in such capacity may direct the voting and disposition of the shares held by Cambrian, subject in certain instances to the approval of Cambrian's Board of Directors. Mr. Peyer disclaims beneficial ownership of such shares. The shares subject to the option vest and become exercisable in 12 equal monthly installments over a one year period such that the option is fully vested on the first anniversary of the date of grant, or July 10, 2024, subject to the Reporting Person's continuous service with the Issuer as of each such vesting date; provided that the option will in any case be fully vested on the date of the Company's next annual stockholder meeting, subject to the Reporting Person's continuous service with the Issuer through such vesting date. /s/ James Peyer 2023-07-12