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

Rhea-AI Filing Summary

Day One Biopharmaceuticals granted its Chief Commercial Officer, Lauren Merendino, new equity awards dated January 30, 2026. She received a stock option for 110,000 shares of common stock at an exercise price of $11.16 per share. The option vests in 1/48th monthly, starting February 28, 2026, as long as she continues providing service on each vesting date.

Merendino also received 74,000 Restricted Stock Units (RSUs). Each RSU represents a right to one share of common stock upon settlement and vests in 1/16th quarterly installments on February 15, May 15, August 15 and November 15, subject to continued service. RSUs either vest or are canceled before the vesting date and do not have a traditional expiration date.

Insider Trade Summary

2 transactions reported

Mixed 2 txns

Insider Merendino Lauren

Role Chief Commercial Officer

Type	Security	Shares	Price	Value
Grant/Award	Stock Option (right to buy Common Stock)	110,000	$0.00	--
Grant/Award	Restricted Stock Units	74,000	$0.00	--

Holdings After Transaction: Stock Option (right to buy Common Stock) — 110,000 shares (Direct); Restricted Stock Units — 74,000 shares (Direct)

Footnotes (1)

1. 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. Each Restricted Stock Unit ("RSU") represents a contingent right to receive one share of the Issuer's Common Stock upon settlement. 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. RSUs do not expire; they either vest or are canceled prior to the vesting date.

Form 4 Insider Transactions: What Each Field Means →

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

OMB APPROVAL

OMB Number:			3235-0287
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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)
01/30/2026

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

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
Stock Option (right to buy Common Stock)	$11.16	01/30/2026		A		110,000		(1)	01/29/2036	Common Stock	110,000	$0	110,000	D
Restricted Stock Units	(2)	01/30/2026		A		74,000		(3)	(4)	Common Stock	74,000	$0	74,000	D

Explanation of Responses:

1. 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.

2. Each Restricted Stock Unit ("RSU") represents a contingent right to receive one share of the Issuer's Common Stock upon settlement.

3. 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.

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

	/s/ Charles N. York II, as Attorney-in-Fact	01/30/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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