Sec Form 3 Filing - CLACKSON TIMOTHY P @ Xilio Therapeutics, Inc. - 2021-10-21

FORM 3 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 CLACKSON TIMOTHY P 2. Issuer Name and Ticker or Trading Symbol Xilio Therapeutics, Inc. [ XLO] 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) C/O XILIO THERAPEUTICS, INC., 828 WINTER STREET, SUITE 300 3. Date of Earliest Transaction (MM/DD/YY) 10/21/2021 (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 Common Stock 20,068 D Common Stock 70,888 I The Timothy P. Clackson Irrevocable GST Trust of 2020

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) $ 5.51 ( 1 ) 01/15/2022 Common Stock 7,525 D Stock Option (right to buy) $ 5.51 ( 2 ) 01/15/2022 Common Stock 2,776 D Stock Option (right to buy) $ 5.51 ( 3 ) 01/15/2022 Common Stock 5,281 D Stock Option (right to buy) $ 5.89 ( 4 ) 01/15/2022 Common Stock 5,213 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other CLACKSON TIMOTHY P C/O XILIO THERAPEUTICS, INC. 828 WINTER STREET, SUITE 300 WALTHAM,, MA02451 X Signatures /s/ Timothy Clackson 10/21/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The option was granted on July 23, 2020 for 32,846 shares. On May 21, 2019, 25% of the shares underlying the option vested and the remaining shares shall vest in equal monthly installments until May 21, 2022. ( 2 )The option was granted on July 23, 2020 for 11,104 shares. On June 14, 2020, 25% of the shares underlying the option vested and the remainder shall vest in equal monthly installments thereafter until June 14, 2023. ( 3 )The option was granted on July 23, 2020 for 23,045 shares. The shares began vesting on March 12, 2020 and shall vest in equal monthly installments until February 12, 2024. ( 4 )The option was granted on March 11, 2021 for 35,752 shares. The shares underlying the option began vesting on April 1, 2021 and shall vest in equal monthly installments thereafter until March 1, 2025.

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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