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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1. Name and Address of Reporting Person * AI Day1 LLC 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 __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O ACCESS INDUSTRIES, INC., 40 WEST 57TH STREET, 28TH FLOOR 3. Date of Earliest Transaction (Month/Day/Year) 04/23/2026 (Street) NEW YORK, NY 10019 4. If Amendment, Date Original Filed (Month/Day/Year) 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 (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 U(1) 12,929,322(1) D $21.5 0 D(2)

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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

Pre-Funded Warrant (right to buy)

$0.0001

04/23/2026

D(1)

827,586(1)

(3)

(3)

Common Stock

827,586

$21.4999

0

D(2)

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
AI Day1 LLC C/O ACCESS INDUSTRIES, INC. 40 WEST 57TH STREET, 28TH FLOOR NEW YORK, NY 10019		X
Access Industries Holdings LLC C/O ACCESS INDUSTRIES, INC. 40 WEST 57TH STREET, 28TH FLOOR NEW YORK, NY 10019		X
ACCESS INDUSTRIES MANAGEMENT, LLC C/O ACCESS INDUSTRIES, INC. 40 WEST 57TH STREET, 28TH FLOOR NEW YORK, NY 10019		X
Blavatnik Len C/O ACCESS INDUSTRIES, INC. 40 WEST 57TH STREET, 28TH FLOOR NEW YORK, NY 10019		X

Signatures

/s/ Alejandro Moreno for AI Day1 LLC		04/27/2026
**Signature of Reporting Person		Date
/s/ Alejandro Moreno for Access Industries Holdings LLC		04/27/2026
**Signature of Reporting Person		Date
/s/ Alejandro Moreno for Access Industries Management, LLC		04/27/2026
**Signature of Reporting Person		Date
/s/ Alejandro Moreno, as Attorney-in-Fact for Mr. Blavatnik		04/27/2026
**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 April 9, 2026, AI Day1 tendered all of its shares of Common Stock pursuant to the tender offer by Servier Detroit Inc. ("Purchaser") to purchase all of the issued and outstanding shares of Common Stock for $21.50 per share in cash, upon the terms and subject to the conditions described in the Offer to Purchase and related Letter of Transmittal filed with the SEC on Schedule TO on March 26, 2026. Such shares were accepted by the Purchaser on April 23, 2026. On April 23, 2026, in connection with the consummation of the merger, each pre-funded warrant held by AI Day1 to purchase Common Stock was converted into the right to receive $21.4999 per warrant in cash.
(2)	The securities reported are held directly by AI Day1 LLC ("AI Day1") and may be deemed to be beneficially owned by Access Industries Holdings LLC ("AIH"), Access Industries Management, LLC ("AIM") and Len Blavatnik because (i) Mr. Blavatnik controls AIM and AIH, (ii) AIM controls AIH, and (iii) AIH owns all of the voting units of AI Day1. Each of AIH, AIM and Mr. Blavatnik, and each of their affiliated entities and the officers, partners, members and managers thereof, disclaims beneficial ownership of these securities, except to the extent of its or his pecuniary interest therein, and this form shall not be construed as an admission that any such reporting person is the beneficial owner of any of the securities reported on this form.
(3)	Each pre-funded warrant is exercisable at any time after the date of issuance and the pre-funded warrants do not expire. The pre-funded warrants are not exercisable to the extent that the aggregate number of shares of Common Stock beneficially owned by AI Day1 LLC, including together with its direct or indirect affiliates, any person acting or who could be deemed to be acting as a group together with the holder, and any other persons whose beneficial ownership of the Common Stock would or could be aggregated with the holder's for the purposes of Section 13(d) or Section 16 of the Exchange Act of 1934, as amended, immediately following such exercise would exceed 9.99%; provided, however, that AI Day1 LLC may increase or decrease the beneficial ownership limitation by giving 61 days' notice to the Issuer, but not to exceed any percentage in excess of 19.99%.

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