On September 23, 2025, the Company announced that it implemented cost reduction actions, including decreasing its workforce by approximately 25%. During the year ended December 31, 2025, the Company incurred approximately $1,027 in restructuring costs, primarily related to severance costs. These costs were paid out in the fourth quarter of 2025.

On November 2, 2023, the Company announced a restructuring plan to prioritize the commercialization of VOWST and the completion of the SER-155 Phase 1b study, while significantly reducing costs and supporting longer-term business sustainability. The restructuring plan included (i) a reduction of the Company’s workforce by approximately 41% across the organization, resulting in the elimination of approximately 160 positions; (ii) significantly scaling back all non-partnered research and development activities other than the completion of the SER-155 Phase 1b study; and (iii) reducing general and administrative expenses, including consolidating office space.

During the year ended December 31, 2023, the Company recognized a restructuring charge of $5,606, which was incurred entirely in the fourth quarter of 2023, and which represents all restructuring charges expected to be incurred. $3,481 of the total restructuring charges was included in research and development expenses and the remaining $2,125 in general and administrative expenses in the accompanying consolidated statements of operations and comprehensive income (loss) for the year ended December 31, 2023. Restructuring charges included approximately $5,345 of employee related termination costs in the form of salary continuation and cash severance payments, and $261 related to the acceleration of vesting of certain previously granted RSUs and PSUs.

The unpaid restructuring charge included in accrued expenses and other current liabilities in the Company’s consolidated balance sheets was $0 and $20 for the years ended December 31, 2025 and 2024, respectively.