Initial Statement of Beneficial Ownership (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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(Print or Type Responses)

1. Name and Address of Reporting Person * Atay Oguzhan 2. Date of Event Requiring Statement (Month/Day/Year) 11/05/2025 3. Issuer Name and Ticker or Trading Symbol BillionToOne, Inc. [BLLN] (Last) (First) (Middle) C/O BILLIONTOONE, INC., 1035 O'BRIEN DRIVE 4. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) See Remarks 5. If Amendment, Date Original Filed (Month/Day/Year) (Street) MENLO PARK, CA 94025 6. Individual or Joint/Group Filing (Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) 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) Common Stock(1) 1,965,108 D Common Stock(2) 200,000 I By spouse(3)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.			SEC 1473 (7-02)
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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 of Derivative Security: 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
Series A-1 Convertible Preferred Stock	(4)	(4)	Common Stock(4)	262,434	(4)	D
Stock Option (right to buy)	(5)	06/07/2031	Common Stock(2)	640,000	$2.8	D
Stock Option (right to buy)	(6)	06/18/2035	Common Stock(2)	1,003,102	$20.04	D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Atay Oguzhan C/O BILLIONTOONE, INC. 1035 O'BRIEN DRIVE MENLO PARK, CA 94025	X		See Remarks

Signatures

/s/ Thomas P. Lynch, Attorney-in-Fact		11/05/2025
**Signature of Reporting Person		Date

Explanation of Responses:

*	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).
(1)	Immediately prior to the completion of the Issuer's initial public offering of Class A common stock (the "Offering"), each share of Common Stock shall be reclassified into one share of Class A common stock and such shares of Class A common stock shall be exchanged at a 1:1 ratio for shares of Class B common stock.
(2)	Immediately prior to the completion of the Offering, each share of Common Stock shall be reclassified into one share of Class A common stock.
(3)	Represents shares held directly by the Reporting Person's spouse.
(4)	The reported security is convertible into the Issuer's Common Stock on a one-for-one basis at any time at the holder's election and shall automatically convert into Class A common stock immediately prior to the completion of the Offering without payment of further consideration. The shares have no expiration date. Immediately prior to the completion of the Offering, such shares of Class A common stock shall be exchanged at a 1:1 ratio for shares of Class B common stock.
(5)	The options are fully vested and exercisable.
(6)	The options are subject to a service-based vesting requirement, which shall be satisfied over a six-year period. The options vest and become exercisable in equal monthly installments commencing on June 11, 2025, subject to the Reporting Person's continuous service with the Issuer through each such vesting date.
Remarks: Chairman and Chief Executive Officer Exhibit 24 - Power of Attorney

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