Sec Form 4 Filing - MILLENNIUM MANAGEMENT LLC @ Sensei Biotherapeutics, Inc. - 2026-03-26

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person MILLENNIUM MANAGEMENT LLC 2. Issuer Name and Ticker or Trading Symbol Sensei Biotherapeutics, Inc. [ SNSE] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 399 PARK AVENUE, 3. Date of Earliest Transaction (MM/DD/YY) 03/26/2026 (Street) NEW YORK, NY10022 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 03/26/2026 P 778 A $ 27.2267 ( 1 ) 131,370 ( 2 ) I See footnote ( 3 ) Common Stock 03/26/2026 P 1,327 A $ 27.9467 ( 4 ) 131,370 ( 2 ) I See footnote ( 3 ) Common Stock 03/26/2026 P 2,601 A $ 28.8539 ( 5 ) 131,370 ( 2 ) I See footnote ( 3 ) Common Stock 03/26/2026 P 1,025 A $ 29.9788 ( 6 ) 131,370 ( 2 ) I See footnote ( 3 ) Common Stock 03/26/2026 S 583 D $ 26.8797 ( 7 ) 131,370 ( 2 ) I See footnote ( 3 ) Common Stock 03/26/2026 S 1,274 D $ 28.6882 ( 8 ) 131,370 ( 2 ) I See footnote ( 3 ) Common Stock 03/27/2026 P 10,643 A $ 26.2933 ( 9 ) 142,360 ( 2 ) I See footnote ( 3 ) Common Stock 03/27/2026 P 4,384 A $ 27.2826 ( 10 ) 142,360 ( 2 ) I See footnote ( 3 ) Common Stock 03/27/2026 P 294 A $ 28.1301 ( 11 ) 142,360 ( 2 ) I See footnote ( 3 ) Common Stock 03/27/2026 S 469 D $ 26.7652 ( 12 ) 142,360 ( 2 ) I See footnote ( 3 ) Common Stock 03/27/2026 S 36 D $ 27.369 ( 13 ) 142,360 ( 2 ) I See footnote ( 3 ) Common Stock 03/30/2026 P 2,992 A $ 25.0784 ( 14 ) 145,678 ( 2 ) I See footnote ( 3 ) Common Stock 03/30/2026 P 4,995 A $ 25.99 ( 15 ) 145,678 ( 2 ) I See footnote ( 3 ) Common Stock 03/30/2026 P 1,176 A $ 26.7 ( 16 ) 145,678 ( 2 ) I See footnote ( 3 ) Common Stock 03/30/2026 P 370 A $ 27.68 ( 17 ) 145,678 ( 2 ) I See footnote ( 3 ) Common Stock 03/30/2026 S 518 D $ 25.8501 ( 18 ) 145,678 ( 2 ) I See footnote ( 3 ) Common Stock 03/30/2026 S 370 D $ 27.68 ( 19 ) 145,678 ( 2 ) I See footnote ( 3 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other MILLENNIUM MANAGEMENT LLC 399 PARK AVENUE NEW YORK, NY10022 X ICS OPPORTUNITIES II LLC C/O MILLENNIUM MANAGEMENT LLC 399 PARK AVENUE NEW YORK, NY10022 X MILLENNIUM GROUP MANAGEMENT LLC 399 PARK AVENUE NEW YORK, NY10022 X ENGLANDER ISRAEL A C/O MILLENNIUM MANAGEMENT LLC 399 PARK AVENUE NEW YORK, NY10022 X Signatures MILLENNIUM MANAGEMENT LLC: By: /s/ Gil Raviv, Global General Counsel 05/14/2026 Signature of Reporting Person Date ICS OPPORTUNITIES II LLC, By: Millennium Management LLC, its Investment Manager: By: /s/ Gil Raviv, Global General Counsel 05/14/2026 Signature of Reporting Person Date MILLENNIUM GROUP MANAGEMENT LLC: By: /s/ Gil Raviv, Global General Counsel 05/14/2026 Signature of Reporting Person Date /s/ Israel A. Englander 05/14/2026 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents volume-weighted average price ("VWAP") of purchases of 778 shares of common stock ("Common Stock"), par value $0.0001 per share, of Sensei Biotherapeutics, Inc. (the "Company") on March 26, 2026 at prices ranging from $26.66 to $27.62. Upon request by the Commission staff, the Company, or a security holder of the Company, the reporting persons will provide full information regarding the number of shares purchased or sold by the reporting person at each separate price within each range represented by a VWAP disclosed herein. ( 2 )In each case, the number of shares of the Company's Common Stock disclosed in column 5 is the number of shares of the Company's Common Stock beneficially owned by Millennium Management LLC at the conclusion of the transactions on the date disclosed in the corresponding entry in column 2. ( 3 )The transactions in the Company's Common Stock reported herein were made by ICS Opportunities II LLC or other trading entities, in each case subject to voting control and investment discretion by Millennium Management LLC, Millennium Group Management LLC (the managing member of Millennium Management LLC) and Israel A. Englander (the sole voting trustee of the managing member of Millennium Group Management LLC). Each reporting person disclaims beneficial ownership of the shares of the Company's Common Stock disclosed herein except to the extent of such reporting person's pecuniary interest therein, if any. ( 4 )Represents VWAP of purchases of 1,327 shares of the Company's Common Stock on March 26, 2026 at prices ranging from $27.70 to $28.4163. ( 5 )Represents VWAP of purchases of 2,601 shares of the Company's Common Stock on March 26, 2026 at prices ranging from $28.7072 to $29.51. ( 6 )Represents VWAP of purchases of 1,025 shares of the Company's Common Stock on March 26, 2026 at prices ranging from $29.79 to $30.105. ( 7 )Represents VWAP of sales of 583 shares of the Company's Common Stock on March 26, 2026 at prices ranging from $26.68 to $27.4650. ( 8 )Represents VWAP of sales of 1,274 shares of the Company's Common Stock on March 26, 2026 at prices ranging from $28.07 to $28.7651. ( 9 )Represents VWAP of purchases of 10,643 shares of the Company's Common Stock on March 27, 2026 at prices ranging from $25.9197 to $26.88. ( 10 )Represents VWAP of purchases of 4,384 shares of the Company's Common Stock on March 27, 2026 at prices ranging from $26.9750 to $27.68. ( 11 )Represents VWAP of purchases of 294 shares of the Company's Common Stock on March 27, 2026 at prices ranging from $28.10 to $28.60. ( 12 )Represents VWAP of sales of 469 shares of the Company's Common Stock on March 27, 2026 at prices ranging from $26.21 to $26.95. ( 13 )Represents VWAP of sales of 36 shares of the Company's Common Stock on March 27, 2026 at prices ranging from $27.2322 to $27.68. ( 14 )Represents VWAP of purchases of 2,992 shares of the Company's Common Stock on March 30, 2026 at prices ranging from $24.495 to $25.1856. ( 15 )Represents VWAP of purchases of 4,995 shares of the Company's Common Stock on March 30, 2026 at prices ranging from $25.50 to $26.48. ( 16 )Represents VWAP of purchases of 1,176 shares of the Company's Common Stock on March 30, 2026 at prices ranging from $26.50 to $26.90. ( 17 )Represents purchases of 370 shares of the Company's Common Stock on March 30, 2026 at $27.68 per share. ( 18 )Represents VWAP of sales of 518 shares of the Company's Common Stock on March 30, 2026 at prices ranging from $25.13 to $26.0734. ( 19 )Represents sales of 370 shares of the Company's Common Stock on March 30, 2026 at $27.68 per share.

Remarks: Assuming, without conceding, the application of Section 16(b) of the Securities Exchange Act of 1934, the reporting persons have disgorged to the Company all amounts that could be deemed profit realized by them from the transactions in the Company's Common Stock reported on this Form 4 and the other two statements on Form 4 filed by Millennium Management LLC on the same date.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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