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 * Ileri Firat 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) SQUARE VICTORIA REGAIN 1 4. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) 5. If Amendment, Date Original Filed (Month/Day/Year) (Street) SINT-JOOST-TEN-NODE, C9 1210 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) 179,999 I See footnotes(2)(8)

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-6 Convertible Preferred Stock	(3)	(3)	Common Stock(1)	28,981	(3)	D
Series B-2 Convertible Preferred Stock	(3)	(3)	Common Stock(1)	640,727	(3)	I	See footnotes(4)(8)
Series B-1 Convertible Preferred Stock	(3)	(3)	Common Stock(1)	18,845	(3)	I	See footnotes(5)(8)
Series C Convertible Preferred Stock	(3)	(3)	Common Stock(1)	1,569,015	(3)	I	See footnotes(6)(8)
Series D Convertible Preferred Stock	(3)	(3)	Common Stock(1)	446,103	(3)	I	See footnotes(6)(8)
Series A-1 Convertible Preferred Stock	(3)	(3)	Common Stock(1)	20,000	(3)	I	See footnotes(2)(8)
Series A-2 Convertible Preferred Stock	(3)	(3)	Common Stock(1)	33,000	(3)	I	See footnotes(2)(8)
Series B-1 Convertible Preferred Stock	(3)	(3)	Common Stock(1)	2,261,377	(3)	I	See footnotes(2)(8)
Series C Convertible Preferred Stock	(3)	(3)	Common Stock(1)	137,288	(3)	I	See footnotes(2)(8)
Series A-6 Convertible Preferred Stock	(3)	(3)	Common Stock(1)	2,260,520	(3)	I	See footnotes(7)(8)
Series B-2 Convertible Preferred Stock	(3)	(3)	Common Stock(1)	320,363	(3)	I	See footnotes(7)(8)

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Ileri Firat SQUARE VICTORIA REGAIN 1 SINT-JOOST-TEN-NODE, C9 1210	X	X

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.
(2)	The reported security is directly held by Hummingbird Opportunity Fund II CommV.
(3)	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 closing of the Offering without payment of further consideration. The shares have no expiration date.
(4)	The reported security is directly held by HB&Q NV (HB&Q COMPARTMENT III).
(5)	The reported security is directly held by Hummingbird Collective CommV.
(6)	The reported security is directly held by Hummingbird Dragons CommV.
(7)	The reported security is directly held by Hummingbird Ventures III CommV.
(8)	Humming Bird Ventures Management NV is the managing member of Hummingbird Opportunity Fund II CommV, Hummingbird Ventures III CommV, Hummingbird Dragons CommV, Hummingbird Collective CommV, and HB&Q NV (HB&Q COMPARTMENT III) (the Hummingbird Funds) and, as a result, may be deemed to beneficially own shares held by the Hummingbird Funds. Firat Ileri, Barend Van den Brande, and Lukas Decoster are partners of Hummingbird Ventures Management NV and may be deemed to have shared voting and investment power over the shares held by the Hummingbird Funds. The Reporting Person disclaims beneficial ownership of these shares except to the extent of his pecuniary interest therein.
Remarks: Exhibit 24 - Power of Attorney

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