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 * Merendino Lauren 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) Chief Commercial Officer (Last) (First) (Middle) 1800 SIERRA POINT PARKWAY, SUITE 200 3. Date of Earliest Transaction (Month/Day/Year) 04/23/2026 (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 04/23/2026 D 60,157 D (1)(2) 0 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
Stock Option (right to buy Common Stock)	$8.99	04/23/2026		D			330,200	(3)	06/11/2033	Common Stock	330,200	(4)	0	D
Stock Option (right to buy Common Stock)	$8.99	04/23/2026		D			90,000	(5)	01/04/2034	Common Stock	90,000	(4)	0	D
Stock Option (right to buy Common Stock)	$8.99	04/23/2026		D			90,000	(6)	01/14/2035	Common Stock	90,000	(4)	0	D
Stock Option (right to buy Common Stock)	$11.16	04/23/2026		D			110,000	(7)	01/29/2036	Common Stock	110,000	(4)	0	D
Restricted Stock Unit (RSU)	(8)	04/23/2026		D			18,978	(9)	(10)	Common Stock	18,978	(4)	0	D
Restricted Stock Unit (RSU)	(8)	04/23/2026		D			25,816	(11)	(10)	Common Stock	25,816	(4)	0	D
Restricted Stock Unit (RSU)	(8)	04/23/2026		D			40,565	(11)	(10)	Common Stock	40,565	(4)	0	D
Restricted Stock Unit (RSU)	(8)	04/23/2026		D			69,375	(11)	(10)	Common Stock	69,375	(4)	0	D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Merendino Lauren 1800 SIERRA POINT PARKWAY, SUITE 200 BRISBANE, CA 94005			Chief Commercial Officer

Signatures

/s/ Charles N. York II, as Attorney-in-Fact		04/23/2026
**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)	On March 6, 2026, Servier Pharmaceuticals LLC, a Delaware limited liability company ("Parent"), Servier Detroit Inc., a Delaware corporation and a wholly owned subsidiary of Parent ("Merger Sub"), Day One Biopharmaceuticals, Inc., a Delaware corporation (the "Company"), and Servier S.A.S., a French societe par actions simplifiee, solely as a guarantor, entered into an Agreement and Plan of Merger (the "Merger Agreement"). Pursuant to the Merger Agreement, the Merger Sub merged with and into the Company (such merger and the other transactions contemplated by the Merger Agreement, the "Merger") with the Company surviving the Merger as a wholly owned subsidiary of the Parent.
(2)	Upon the closing of the Merger on April 23, 2026, each issued and outstanding share of the Company's Common Stock, par value $0.0001 per share, was either (x) purchased for $21.50 per share (the "Offer Price"), net to the seller in cash, without interest, and subject to applicable withholding taxes, on the terms and conditions set forth in the Merger Agreement, or (y) automatically converted into the right to receive the Offer Price (the "Merger Consideration"), net to the seller in cash, without interest, and subject to applicable withholding taxes, on the terms and conditions set forth in the Merger Agreement.
(3)	The option vests as to 25% of the total shares on June 12, 2024 and then 2.0833% of the total shares vest monthly thereafter, with 100% of the total shares vested on June 12, 2027, subject to the Reporting Person's provision of service to the Issuer on each vesting date.
(4)	Immediately prior to the effective time of the Merger, all outstanding unvested stock options and unvested restricted stock units became fully vested. At the effective time of the Merger, each stock option and restricted stock unit was canceled and converted into the right to receive an amount in cash equal to the Merger Consideration (or, in the case of stock options, the difference between the Merger Consideration and the applicable per share exercise price), less any applicable withholding taxes.
(5)	The option vests as to 1/48th of the total shares monthly, commencing February 5, 2024, subject to the Reporting Person's provision of service to the Issuer on each vesting date.
(6)	The option vests as to 1/48th of the total shares monthly, commencing February 15, 2025, subject to the Reporting Person's provision of service to the Issuer on each vesting date.
(7)	The option vests as to 1/48th of the total shares monthly, commencing February 28, 2026, subject to the Reporting Person's provision of service to the Issuer on each vesting date.
(8)	Each Restricted Stock Unit ("RSU") represents a contingent right to receive one share of the Issuer's Common Stock upon settlement for no consideration.
(9)	The RSUs vested as to 1/4th of the total award on August 15, 2024, and the remaining 3/4 of the award vests in 12 substantially equal quarterly installments thereafter on November 15, February 15, May 15 and August 15, subject to the Reporting Person's provision of service to the Issuer on each vesting date.
(10)	RSUs do not expire; they either vest or are canceled prior to the vesting date.
(11)	The RSUs 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.

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