Statement of Changes in Beneficial Ownership (Form 4)

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b). Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

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

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(Print or Type Responses)

1. Name and Address of Reporting Person * York Charles N II 2. Issuer Name and Ticker or Trading Symbol Day One Biopharmaceuticals, Inc. [DAWN] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) COO and CFO (Last) (First) (Middle) 1800 SIERRA POINT PARKWAY, SUITE 200 3. Date of Earliest Transaction (Month/Day/Year) 08/15/2025 (Street) BRISBANE, CA 94005 4. If Amendment, Date Original Filed (Month/Day/Year) 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 (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 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 08/15/2025 M 1,375 A (1) 266,606 D Common Stock 08/15/2025 M 2,250 A (1) 268,856 D Common Stock 08/15/2025 M 6,625 A (1) 275,481 D Common Stock 08/15/2025 M 6,625 A (1) 282,106 D Common Stock 08/18/2025 S(2) 4,106 D $6.7671(3) 278,000 D

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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 (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	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 (Month/Day/Year)		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
Restricted Stock Unit (RSU)	(1)	08/15/2025		M			1,375	(4)	(5)	Common Stock	1,375	$ 0	1,375	D
Restricted Stock Unit (RSU)	(1)	08/15/2025		M			2,250	(4)	(5)	Common Stock	2,250	$ 0	11,250	D
Restricted Stock Unit (RSU)	(1)	08/15/2025		M			6,625	(4)	(5)	Common Stock	6,625	$ 0	59,625	D
Restricted Stock Unit (RSU)	(1)	08/15/2025		M			6,625	(4)	(5)	Common Stock	6,625	$ 0	86,125	D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
York Charles N II 1800 SIERRA POINT PARKWAY, SUITE 200 BRISBANE, CA 94005			COO and CFO

Signatures

/s/ Charles N. York II		08/19/2025
**Signature of Reporting Person		Date

Explanation of Responses:

*	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).
(1)	Each Restricted Stock Unit ("RSU") represents a contingent right to receive one share of the Issuer's Common Stock upon settlement for no consideration.
(2)	The sale of shares is for the sole purpose of covering the Reporting Person's tax liability with respect to the settlement of RSUs.
(3)	The price reported in Column 4 is a weighted average price. These shares were sold as part of block trades for multiple security holders of the Issuer at prices ranging from $6.65 to $6.87, inclusive. The Reporting Person undertakes to provide to the Issuer, any securityholder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth herein with regard to the block trade.
(4)	The RSUs will vest as to 1/16th of the total award in quarterly installments on February 15, May 15, August 15 and November 15, subject to the Reporting Person's provision of service to the Issuer on each vesting date.
(5)	RSUs do not expire; they either vest or are canceled prior to the vesting date.

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