[Form 4] Day One Biopharmaceuticals, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Day One Biopharmaceuticals (DAWN) reported insider equity activity by its Chief Commercial Officer on a Form 4. On 11/15/2025, several batches of Restricted Stock Units (RSUs) converted into a total of 10,536 shares of common stock through multiple transactions coded "M". Following these RSU settlements, the officer beneficially owned 54,535 shares of common stock directly.

On 11/17/2025, the officer sold 3,726 shares of common stock in a transaction coded "S" at a weighted average price of $8.9147 per share, as part of block trades executed in a price range from $8.545 to $9.305. The filing states that this sale was made solely to cover tax liabilities arising from the RSU settlements. The RSUs vest in quarterly installments over time, subject to continued service, and do not have an expiration date.

SEC Form 4

FORM 4

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
or Section 30(h) of the Investment Company Act of 1940

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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 for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Merendino Lauren

(Last) (First) (Middle)

1800 SIERRA POINT PARKWAY, SUITE 200

(Street)

BRISBANE CA 94005

(City) (State) (Zip)

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

3. Date of Earliest Transaction (Month/Day/Year)
11/15/2025

4. If Amendment, Date of 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

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	11/15/2025		M		3,162	A	(1)	47,161(2)	D
Common Stock	11/15/2025		M		3,687	A	(1)	50,848	D
Common Stock	11/15/2025		M		3,687	A	(1)	54,535	D
Common Stock	11/17/2025		S(3)		3,726	D	$8.9147(4)	50,809	D

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 Securities Underlying Derivative Security (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: 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)	11/15/2025		M			3,162	(5)	(6)	Common Stock	3,162	$0	22,140	D
Restricted Stock Unit (RSU)	(1)	11/15/2025		M			3,687	(7)	(6)	Common Stock	3,687	$0	29,504	D
Restricted Stock Unit (RSU)	(1)	11/15/2025		M			3,687	(7)	(6)	Common Stock	3,687	$0	44,252	D

Explanation of Responses:

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. Includes 2,068 shares of Common Stock acquired by the Reporting Person on May 15, 2025 pursuant to the Issuer's employee stock purchase plan.

3. The sale of shares is for the sole purpose of covering the Reporting Person's tax liability with respect to the settlement of RSUs.

4. 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 $8.545 to $9.305, 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.

5. 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.

6. RSUs do not expire; they either vest or are canceled prior to the vesting date.

7. 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.

	/s/ Charles N. York II, as Attorney-in-Fact	11/18/2025
	** Signature of Reporting Person	Date
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).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What insider transaction did Day One Biopharmaceuticals (DAWN) report?

The Chief Commercial Officer of Day One Biopharmaceuticals (DAWN) reported RSU settlements into common stock on 11/15/2025 and a subsequent stock sale on 11/17/2025 on a Form 4.

How many Day One Biopharmaceuticals (DAWN) shares were sold by the insider?

The officer sold 3,726 shares of Day One Biopharmaceuticals common stock on 11/17/2025 in a single reported sale transaction.

At what price were the DAWN shares sold in the Form 4 transaction?

The sale was reported at a weighted average price of $8.9147 per share, with block trades executed in a range from $8.545 to $9.305 per share.

Why did the Day One Biopharmaceuticals officer sell shares?

The Form 4 states that the 3,726-share sale was made solely to cover the reporting person’s tax liability related to the settlement of RSUs.

How many DAWN shares did the insider beneficially own after the transactions?

After the reported transactions, the officer beneficially owned 50,809 shares of Day One Biopharmaceuticals common stock directly.

How do the Day One Biopharmaceuticals RSUs vest for this officer?

One RSU grant vested 1/4 on August 15, 2024 with the remaining 3/4 vesting in 12 substantially equal quarterly installments, while another vests in 1/16 installments each quarter, all subject to continued service.