Management Change/Compensation (Form 8-K)

On December 22, 2025, Sensei Biotherapeutics, Inc. (the "Company") entered into Retention Agreements with Christopher Gerry, its President and Principal Executive Officer, and Josiah Craver, its Senior Vice President of Finance and Principal Finance and Accounting Officer (the "Retention Agreements"), which amend in part the compensatory provisions of their existing employment agreements with the Company. Pursuant to the Retention Agreements, the Company agreed that the annual base salaries for Messrs. Gerry and Craver would be $425,000 and $400,000, respectively, each effective as of November 14, 2025. Messrs. Gerry and Craver are also eligible to receive an annual target bonus equal to 40% of their respective base salaries beginning with the year ending December 31, 2026.

In addition, pursuant to the Retention Agreements, Messrs. Gerry and Craver are eligible for retention bonuses as follows: (i) a first retention bonus equal to their full target annual bonus for 2025 if (a) they remain employed at the Company through February 13, 2026 or (b) they are terminated without cause or resign for good reason prior to February 13, 2026 not in connection with a change in control; and (ii) a second retention bonus equal to their target annual bonus for 2026 pro rated for the number of months such employee was employed during 2026 if they are terminated without cause or resign for good reason prior to the payment of 2026 bonuses; provided that if the termination without cause or resignation for good reason does not occur in connection with a change in control, then such employee will be entitled to two times the second retention bonus payment.

The foregoing severance benefits are contingent upon the executive timely executing a separation agreement and release of claims against the Company.

The foregoing description of the Retention Agreements do not purport to be complete and are qualified by reference to the full text of each agreement, copies of which will be filed as exhibits to the Company's Annual Report on Form 10-Kfor the year ending December 31, 2025.

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