Lauren Merendino - 15 Feb 2026 Form 4 Insider Report for Day One Biopharmaceuticals, Inc. (DAWN)

Role: Chief Commercial Officer
Signature: /s/ Charles N. York II, as Attorney-in-Fact
Issuer symbol: DAWN
Transactions as of: 15 Feb 2026
Net transactions value: -$67,448
Form type: 4
Filing time: 18 Feb 2026, 17:18:49 UTC
Previous filing: 30 Jan 2026
SEC: View on sec.gov

Reporting Owners (1)

Name	Relationship	Address	Signature	Signature date	CIK
Merendino Lauren	Chief Commercial Officer	1800 SIERRA POINT PARKWAY, SUITE 200, BRISBANE	/s/ Charles N. York II, as Attorney-in-Fact	18 Feb 2026	0001855298

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
transaction	DAWN	Common Stock	Options Exercise		+3,162	+6.2%		53,971	15 Feb 2026	Direct	F1
transaction	DAWN	Common Stock	Options Exercise		+3,688	+6.8%		57,659	15 Feb 2026	Direct	F1
transaction	DAWN	Common Stock	Options Exercise		+3,687	+6.4%		61,346	15 Feb 2026	Direct	F1
transaction	DAWN	Common Stock	Options Exercise		+4,625	+7.5%		65,971	15 Feb 2026	Direct	F1
transaction	DAWN	Common Stock	Sale	$67,448	-5,814	-8.8%	$11.60	60,157	17 Feb 2026	Direct	F2, F3

Derivative Securities (e.g., puts, calls, warrants, options, convertible securities)

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Underlying Class	Amount	Exercise Price	Ownership	Footnotes
transaction	DAWN	Restricted Stock Unit (RSU)	Options Exercise	$0	-3,162	-14%	$0.000000	18,978	15 Feb 2026	Common Stock	3,162		Direct	F1, F4, F5
transaction	DAWN	Restricted Stock Unit (RSU)	Options Exercise	$0	-3,688	-12%	$0.000000	25,816	15 Feb 2026	Common Stock	3,688		Direct	F1, F5, F6
transaction	DAWN	Restricted Stock Unit (RSU)	Options Exercise	$0	-3,687	-8.3%	$0.000000	40,565	15 Feb 2026	Common Stock	3,687		Direct	F1, F5, F6
transaction	DAWN	Restricted Stock Units (RSU)	Options Exercise	$0	-4,625	-6.2%	$0.000000	69,375	15 Feb 2026	Common Stock	4,625		Direct	F1, F5, F6

* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Explanation of Responses:

Id	Content
F1	Each Restricted Stock Unit ("RSU") represents a contingent right to receive one share of the Issuer's Common Stock upon settlement for no consideration.
F2	The sale of shares is for the sole purpose of covering the Reporting Person's tax liability with respect to the settlement of RSUs.
F3	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 $11.195 to $11.8508, 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.
F4	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.
F5	RSUs do not expire; they either vest or are canceled prior to the vesting date.
F6	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.