Sec Form 4 Filing - Russo Rene @ Xilio Therapeutics, Inc. - 2025-11-21

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 Russo Rene 2. Issuer Name and Ticker or Trading Symbol Xilio Therapeutics, Inc. [ XLO] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) PRESIDENT AND CEO (Last) (First) (Middle) 828 WINTER STREET, SUITE 300 3. Date of Earliest Transaction (MM/DD/YY) 11/21/2025 (Street) WALTHAM, MA02451 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ 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

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 Stock Option (right to buy) $ 0.841 11/21/2025( 1 ) A 2,075,000 ( 2 ) 10/07/2035 Common Stock 2,075,000 $ 0 2,075,000 D Stock Option (right to buy) $ 5.51 11/21/2025 D 239,703 ( 3 ) 07/22/2030 Common Stock 239,703 ( 4 ) 0 D Stock Option (right to buy) $ 1.5 11/21/2025 A 239,703 ( 3 ) 07/22/2030 Common Stock 239,703 ( 4 ) 239,703 D Stock Option (right to buy) $ 5.89 11/21/2025 D 473,334 ( 3 ) 03/10/2031 Common Stock 473,334 ( 4 ) 0 D Stock Option (right to buy) $ 1.5 11/21/2025 A 473,334 ( 3 ) 03/10/2031 Common Stock 473,334 ( 4 ) 473,334 D Stock Option (right to buy) $ 11.69 11/21/2025 D 135,134 ( 3 ) 08/22/2031 Common Stock 135,134 ( 4 ) 0 D Stock Option (right to buy) $ 1.5 11/21/2025 A 135,134 ( 3 ) 08/22/2031 Common Stock 135,134 ( 4 ) 135,134 D Stock Option (right to buy) $ 16 11/21/2025 D 50,041 ( 3 ) 10/20/2031 Common Stock 50,041 ( 4 ) 0 D Stock Option (right to buy) $ 1.5 11/21/2025 A 50,041 ( 3 ) 10/20/2031 Common Stock 50,041 ( 4 ) 50,041 D Stock Option (right to buy) $ 13.83 11/21/2025 D 100,000 ( 5 ) 12/21/2031 Common Stock 100,000 ( 4 ) 0 D Stock Option (right to buy) $ 1.5 11/21/2025 A 100,000 ( 5 ) 12/21/2031 Common Stock 100,000 ( 4 ) 100,000 D Stock Option (right to buy) $ 12.66 11/21/2025 D 150,000 ( 6 ) 02/21/2032 Common Stock 150,000 ( 4 ) 0 D Stock Option (right to buy) $ 1.5 11/21/2025 A 150,000 ( 6 ) 02/21/2031 Common Stock 150,000 ( 4 ) 150,000 D Stock Option (right to buy) $ 2.69 11/21/2025 D 350,000 ( 7 ) 12/31/2032 Common Stock 350,000 ( 4 ) 0 D Stock Option (right to buy) $ 1.5 11/21/2025 A 350,000 ( 7 ) 12/31/2032 Common Stock 350,000 ( 4 ) 350,000 D Stock Option (right to buy) $ 2.785 11/21/2025 D 700,000 ( 3 ) 08/15/2033 Common Stock 700,000 ( 4 ) 0 D Stock Option (right to buy) $ 1.5 11/21/2025 A 700,000 ( 3 ) 08/15/2033 Common Stock 700,000 ( 4 ) 700,000 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Russo Rene 828 WINTER STREET SUITE 300 WALTHAM, MA02451 X PRESIDENT AND CEO Signatures /s/ Kevin Brennan, Attorney-in-Fact 11/25/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On October 8, 2025, the Board of Directors (the "Board") approved the adoption of the Xilio Therapeutics, Inc. 2025 Stock Incentive Plan (the "2025 Plan"), subject to stockholder approval of the adoption of the 2025 Plan. On October 8, 2025, the Compensation Committee of the Board granted these options (referred to as "Tranche 1 Options" in the 2025 Plan) to the Reporting Person, subject to stockholder approval of the adoption of the 2025 Plan. The stockholders approved the adoption of the 2025 Plan on November 21, 2025. ( 2 )The options vest in 36 equal monthly installments over the three-year period beginning on December 21, 2025, subject to the Reporting Person's continued service to the registrant through each applicable vesting date. ( 3 )Immediately exercisable. ( 4 )The transactions reported herein reflect a one-time option repricing, effective on November 21, 2025, which reduced the exercise price of each repriced option to $1.50 per share unless such repriced stock option is exercised prior to November 21, 2026, in which case, the original exercise price must be paid (the "Option Repricing"). Except as modified by the Option Repricing, all other terms and conditions of the repriced options, including, without limitation, any provisions with respect to vesting and expiration, remain in full force and effect. ( 5 )This option was granted on December 22, 2021. The shares underlying the option began vesting on January 1, 2022 and continue to vest in equal monthly installments thereafter through December 1, 2025. ( 6 )This option was granted on February 22, 2022. The shares underlying the option began vesting on March 1, 2022 and continue to vest in equal monthly installments thereafter through February 1, 2026. ( 7 )This option was granted on January 1, 2023. The shares underlying the option began vesting on February 1, 2023 and continue to vest in equal monthly installments thereafter through January 1, 2027.

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