[Form 3] Day One Biopharmaceuticals, Inc. Initial Statement of Beneficial Ownership

Rhea-AI Filing Summary

Day One Biopharmaceuticals (DAWN) has filed a Form 3 (Initial Statement of Beneficial Ownership) for Michael Vasconcelles, who has joined the company as Head of Research and Development. The filing date is June 28, 2025, with the triggering event occurring on June 16, 2025.

Key details of the filing:

• The reporting person currently owns no securities (derivative or non-derivative) of the company
• The filing is made individually, not as part of a group
• The reporting person serves as an Officer (Head of Research and Development) but is not a Director or 10% Owner
• The form was signed by Charles N. York II as Attorney-in-Fact on June 18, 2025

This Form 3 filing is a standard regulatory requirement for new officers under Section 16(a) of the Securities Exchange Act of 1934, establishing a baseline for future transactions and holdings reporting.

SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF 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^*

VASCONCELLES MICHAEL

(Last) (First) (Middle)

C/O DAY ONE BIOPHARMACEUTICALS, INC.

1800 SIERRA POINT PARKWAY, SUITE 200

(Street)

BRISBANE CA 94005

(City) (State) (Zip)

2. Date of Event Requiring Statement (Month/Day/Year)
06/16/2025

3. Issuer Name and Ticker or Trading Symbol
Day One Biopharmaceuticals, Inc. [ DAWN ]

4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Head of Research and Dev.

5. 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 Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

No securities are beneficially owned.

	/s/ Charles N. York II, as Attorney-in-Fact	06/18/2025
	** 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 5 (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

Who is the new Head of Research and Development at DAWN (Day One Biopharmaceuticals)?

Michael Vasconcelles was appointed as the Head of Research and Development at Day One Biopharmaceuticals (DAWN), as disclosed in a Form 3 filing dated June 28, 2025.

Does Michael Vasconcelles own any shares in DAWN upon appointment?

According to the Form 3 filing, Michael Vasconcelles does not beneficially own any securities (either direct or derivative) in Day One Biopharmaceuticals (DAWN) at the time of his appointment.

When did Michael Vasconcelles join DAWN as Head of Research and Development?

The Form 3 filing indicates that the date of event requiring the statement was June 16, 2025, which represents when Michael Vasconcelles took on the role of Head of Research and Development at DAWN.

What type of filing relationship does Michael Vasconcelles have with DAWN?

According to the Form 3, Michael Vasconcelles filed as an Officer (specifically as Head of Research and Development) of DAWN, and the filing was made as an individual reporting person rather than as part of a group.