Statement of Changes in Beneficial Ownership (Form 4)

FORM 4 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 that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN 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 * Rai Akshay 2. Issuer Name and Ticker or Trading Symbol BillionToOne, Inc. [BLLN] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 2180 SAND HILL ROAD, STE. 100 3. Date of Earliest Transaction (Month/Day/Year) 11/06/2025 (Street) MENLO PARK, CA 94025 4. If Amendment, Date 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 (City) (State) (Zip) 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 Common Stock 11/06/2025 A 8,333(1) A $ 0 8,333 D Common Stock 11/07/2025 C(2)(3) 2,676 A (3) 11,009 D Common Stock 11/07/2025 C(2)(3) 1,784,414 A (3) 1,784,414 I See Footnote(4) Common Stock 11/07/2025 J(5) 11,009 D (5) 0 D Common Stock 11/07/2025 J(5) 1,784,414 D (5) 0 I See Footnote(4) Class A Common Stock 11/07/2025 J(5) 11,009 A (5) 11,009 D Class A Common Stock 11/07/2025 J(5) 1,784,414 A (5) 1,784,414 I See Footnote(4)

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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 Underlying Securities (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 of Derivative Security: 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

Series D Convertible Preferred Stock

(3)

11/07/2025

C

2,676

(3)

(3)

Common Stock

2,676

(3)

0

D

Series D Convertible Preferred Stock

(3)

11/07/2025

C

1,784,414

(3)

(3)

Common Stock

1,784,414

(3)

0

I

See Footnotes(4)

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Rai Akshay 2180 SAND HILL ROAD, STE. 100 MENLO PARK, CA 94025	X

Signatures

/s/ Thomas P. Lynch, Attorney-in-Fact		11/10/2025
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(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)	Each restricted stock unit (RSU) represents a contingent right to receive one share of the Issuer's Common Stock. The RSUs shall vest over three years in equal annual installments on the anniversary of November 6, 2025, subject to the Reporting Person's continuous service to the Issuer through each such vesting date.
(2)	The total represents shares received upon conversion of shares of Series D Convertible Preferred Stock.
(3)	The reported security converted into the Issuer's Common Stock on a one-for-one basis automatically immediately prior to the closing of the Issuer's initial public offering of Class A common stock (the "Offering") without payment of further consideration. The shares have no expiration date.
(4)	The reported securities are directly held by Wipro Enterprises Private Limited (Wipro), of which Mr. Rai is the nominee/investor director appointed by Wipro Enterprises Limited. Mr. Rai will not have voting or dispositive control of these securities while such securities are held by Wipro and thus disclaims beneficial ownership of such securities.
(5)	Pursuant to a reclassification exempt under Rule 16b-7, each share of Common Stock was automatically reclassified into one share of Class A common stock immediately prior to the completion of the Offering.

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