Sensei Biotherapeutics, Inc.

Item 5. Other Information.

Rule 10b5-1 Trading Plans

During the fiscal quarter ended September 30, 2025, none of our officers or directors, as defined in Rule 16a-1(f), adopted, modified orterminated a “Rule 10b5-1 trading arrangement” or a “non-Rule 10b5-1 trading arrangement,” as those terms are defined in Item 408 of Regulation S-K.

Costs Associated with Exit or Disposal Activities

As part of the cash preservation associated with the strategic review process, our Board of Directors (the “Board”) has approved a reduction in force of approximately 65% of our workforce. The reduction in force is expected to be completed during the fourth quarter of 2025. We estimate that we will incur cash expenditures of $1.6 million, primarily consisting of severance payments and other employee termination-related expenses, which we expect to recognize the majority of such costs in the fourth quarter of 2025. The estimated charges that we expect to incur are subject to a number of assumptions, and actual results may differ materially from these estimates. We may also incur additional costs not currently contemplated due to events that may occur as a result of, or that are associated with, our workforce reduction.

Departure of Directors or Certain Officers; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers

Departure of Named Executive Officers

On November 13, 2025, in connection with the reduction in force described above, our Board determined to terminate John Celebi, our Chief Executive Officer, Edward van der Horst, our Chief Scientific Officer, and Stephanie Krebs, our Chief Business Officer, effective as of 5:30 p.m. ET on November 14, 2025 (the “Effective Time”). Each of Mr. Celebi, Dr. van der Horst and Ms. Krebs will receive severance compensation as provided in each of their respective employment agreements as described in our proxy statement on Schedule 14A filed with the U.S. Securities and Exchange Commission on April 11, 2025.

In addition, each of Mr. Celebi, Dr. van der Horst and Ms. Krebs have entered into Consulting Agreements with the Company (collectively, the “Consulting Agreements”), effective as of November 14, 2025, pursuant to which they will perform consulting services for the Company. The Consultant Agreements will be for a term of six months and can be terminated by either party upon 15 days prior noticeor immediately in the event of a breach which cannot be cured or if either party is accused of a crime or unethical conduct. Under the Consultant Agreements, each of Mr. Celebi, Dr. van der Horst and Ms. Krebs will perform consulting services at a rate of $425 per hour for up to 20 hours per week. The foregoing description of the Consulting Agreements do not purport to be complete and are qualified by reference to the form of consulting agreement filed as an exhibit to this Quarterly Report on Form 10-Q.

Appointment of Christopher W. Gerry as President and Principal Executive Officer

On November 13, 2025, our Board approved the appointment of Christopher W. Gerry as our President and Principal Executive Officer, effective as of the Effective Time.

Mr. Gerry, age 46, has served as our General Counsel since July 2022. Previously, Mr. Gerry was the Deputy General Counsel at AVROBIO, Inc. from January 2021 to July 2022 and was the Associate General Counsel at AVROBIO from November 2019 to January 2021. Prior to that, Mr. Gerry was an associate at Cooley LLP from 2013 to 2019. Mr. Gerry holds a B.A. from Dickinson College and a J.D. from Boston University School of Law.

There are no arrangements or understandings between Mr. Gerry and any other person pursuant to which he was selected as an officer of the Company, and there is no family relationship between Mr. Gerry and any of the Company’s other directors or executive officers. Mr. Gerry is not a party to any transactions of the type listed in Item 404(a) of Regulation S-K.

Resignation of Directors

On November 12, 2025, William Ringo notified the Company of his intent to resign from his duties as a member of the Board, effective November 14, 2025. Mr. Ringo’s resignation was not due to any disagreement with the Company or any matter relating to the Company’s operations, policies, or practices.

On November 12, 2025, James Peyer, Ph.D. notified the Company of his intent to resign from his duties as a member of the Board, effective November 14, 2025. Mr. Peyer’s resignation was not due to any disagreement with the Company or any matter relating to the Company’s operations, policies, or practices.

On November 12, 2025, John Celebi notified the Company of his intent to resign from his duties as a member of the Board, effective November 14, 2025. Mr. Celebi’s resignation was not due to any disagreement with the Company or any matter relating to the Company’s operations, policies, or practices.

Each of Mr. Ringo and Dr. Peyer will receive the full amount of compensation that would otherwise have been due to them for the fourth quarter under the Company’s non-employee director compensation policy. In connection with Mr. Celebi’s, Mr. Ringo’s and Dr. Peyer’s resignations, the Board approved a reduction in the size of the Board from six to three.

In connection with the resignations, effective November 14, 2025, the Board appointed Bob Holmen as Board Chair; appointed Mr. Holmen, Thomas Ricks and Kristian Humer to the Nominating and Corporate Governance Committee; and appointed Mr. Humer as Chair of the Nominating and Corporate Governance Committee and to the Compensation Committee.