X0407 4/A 2023-02-15 2023-02-17 0 0001829802 Sensei Biotherapeutics, Inc. SNSE 0001843539 Celebi John C/O SENSEI BIOTHERAPEUTICS, INC. 451 D STREET, SUITE 710 BOSTON MA 02210 1 1 0 0 President and CEO 0 Common Stock 2023-02-15 4 A 0 51893 0.00 A 110003 D Common Stock 2023-02-15 4 A 0 21300 0.00 A 131303 D Stock Option (Right to Buy) 1.43 2023-02-15 4 A 0 90000 0.00 A 2033-02-14 Common Stock 90000 90000 D This amendment is being filed solely to correct the number of shares beneficially owned. Due to administrative error the original filing did not include shares purchased under the Issuer's Employee Stock Purchase Plan ("ESPP"). 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 are fully vested. Share balance includes stock purchased under the ESPP not previously reported. These shares represent 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, 2024, February 15, 2025, February 15, 2026 and February 15, 2027, subject to the Reporting Person's continuous service with the Issuer as of each such date. 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, 2024, 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 2023-03-29