Cover Page - USD ($) $ in Millions	12 Months Ended
Cover Page - USD ($) $ in Millions	Dec. 31, 2025	Mar. 23, 2026	Jun. 30, 2025
Cover [Abstract]
Document Type	10-K/A
Amendment Flag	true
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	FY
Document Period End Date	Dec. 31, 2025
Current Fiscal Year End Date	--12-31
Entity Interactive Data Current	Yes
Document Annual Report	true
Document Transition Report	false
Entity Central Index Key	0001829802
Entity Registrant Name	Sensei Biotherapeutics, Inc.
Entity File Number	001-39980
Entity Tax Identification Number	83-1863385
Entity Incorporation, State or Country Code	DE
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Address, Address Line One	1405 Research Boulevard
Entity Address, Address Line Two	Suite 125
Entity Address, City or Town	Rockville
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	20850
City Area Code	240
Local Phone Number	243-8000
Entity Emerging Growth Company	true
Trading Symbol	SNSE
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		1,340,281
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Public Float			$ 7.1
ICFR Auditor Attestation Flag	false
Documents Incorporated by Reference [Text Block]	DOCUMENTS INCORPORATED BY REFERENCE 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 10-K.
Document Financial Statement Error Correction [Flag]	false
Entity Ex Transition Period	false
Amendment Description	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.

Sensei Biotherapeutics, Inc. 10-K/A