0001829802 2025-01-01 2025-12-31 0001829802 2026-03-23 0001829802 2025-06-30 shares iso4217:USD true FY Yes 0001829802 Yes MD No No 10-K/A true 2025-12-31 --12-31 2025 false 001-39980 Sensei Biotherapeutics, Inc. DE 83-1863385 1405 Research Boulevard Suite 125 Rockville 20850 240 243-8000 Common Stock, $0.0001 par value per share SNSE NASDAQ Non-accelerated Filer true true false false false false 7100000 1340281 <div style="margin-top:6pt; margin-bottom:0pt; font-size:9pt; font-family:Times New Roman;font-weight:bold;text-align:center">DOCUMENTS INCORPORATED BY REFERENCE </div><div style="margin-top:6pt; margin-bottom:0pt; font-size:9pt; font-family:Times New Roman">Portions of the Registrant’s definitive proxy statement, to be filed pursuant to Regulation 14A under the Securities Exchange Act of 1934, for its 2026 Annual Meeting of Stockholders are incorporated by reference in Part III of this Form <div style="white-space:nowrap;display:inline;">10-K.</div> </div> Explanatory Note Sensei Biotherapeutics, Inc. (the “Company”) is filing this Amendment No. 1 on Form 10-K/A (“Amendment No. 1”) to amend the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2025, which was originally filed with the U.S. Securities and Exchange Commission (the “SEC”) on March 30, 2026 (the “Original Filing”). The purpose of this Amendment No. 1 is to amend and replace in its entirety Part I, Item 1. Business of the Original Filing in response to comments received from the staff of the SEC. In addition, pursuant to Rule 12b-15 under the Securities Exchange Act of 1934, as amended, this Amendment No. 1 contains revised certifications pursuant to Section 302 of the Sarbanes-Oxley Act of 2002, which are attached hereto as Exhibits 31.3 and 31.4. Because no financial statements or other financial information have been included in this Amendment No. 1, paragraph 3 has been omitted from each of the revised Section 302 Certifications, and because this Amendment No. 1 does not contain or amend any disclosure with respect to Items 307 and 308 of Regulation S-K, paragraphs 4 and 5 have been omitted from each of the revised Section 302 certifications. Except as described above, this Amendment No. 1 does not amend, modify, or otherwise update any other information in the Original Filing and does not reflect events occurring after the filing of the Original Filing. Accordingly, this Amendment No. 1 should be read in conjunction with the Original Filing and the Company’s other filings with the SEC.