X0306 4 2022-02-15 0 0001829802 Sensei Biotherapeutics, Inc. SNSE 0001843563 Colgan Erin C/O SENSEI BIOTHERAPEUTICS, INC. 1405 RESEARCH BLVD., SUITE 125 ROCKVILLE MD 20850 0 1 0 0 Chief Financial Officer Common Stock 2022-02-15 4 A 0 21000 0.00 A 21686 D Stock Option (Right to Buy) 4.30 2022-02-15 4 A 0 62000 0.00 A 2032-02-14 Common Stock 62000 62000 D 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 four equal annual installments on each of February 15, 2023, February 15, 2024, February 15, 2025 and February 15, 2026, subject to the Reporting Person's continuous service with the Issuer as of each such date. Includes 686 shares acquired by the Reporting Person pursuant to the Issuer's Employee Stock Purchase Plan. The option shall vest over a period of four years as follows: 25% of the total number of shares subject to the option shall vest on February 15, 2023; and the remainder will vest 1/48th of total number of shares subject to the option monthly thereafter over the remaining three years, subject to the Reporting Person's continuous service with the Issuer as of each such date. /s/ Mark Ballantyne, Attorney-in-Fact 2022-02-17