SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

BillionToOne, Inc.

(Name of Issuer)

Class A common stock, par value $0.00001 per share

(Title of Class of Securities)

090168105

(CUSIP Number)

12/31/2025

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

SCHEDULE 13G

CUSIP No.

090168105

Names of Reporting Persons

Oguzhan Atay

Check the appropriate box if a member of a Group (see instructions)

(a)

(b)

Sec Use Only

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 3,006,861.00
6	Shared Voting Power 200,000.00
7	Sole Dispositive Power 3,006,861.00
8	Shared Dispositive Power 200,000.00

Aggregate Amount Beneficially Owned by Each Reporting Person

3,206,861.00

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

Checkbox not checked

Percent of class represented by amount in row (9)

7.3 %

Type of Reporting Person (See Instructions)

Comment for Type of Reporting Person: Consists of (i) 2,227,542 shares of Class B common stock of the Issuer (as defined in Item 1(a) below) held of record by Oguzhan Atay (the Reporting Person), (ii) 779,319 shares of Class A common stock underlying stock options exercisable within 60 days of the date of this Statement held by the Reporting Person and (iii) 200,000 shares of Class A common stock held of record by the Reporting Person's spouse. Reporting Person disclaims beneficial ownership of securities held by spouse. Each share of Class B common stock is convertible into one share of Class A common stock at the option of the holder. Excludes 863,783 shares of Class A common stock underlying stock options not exercisable within 60 days of the date of this Statement held by the Reporting Person. Ownership percentage based on 44,222,971 shares, which is the sum of (i) 41,216,110 shares of Class A common stock of the Issuer outstanding as of December 5, 2025, as reported by the Issuer in its quarterly report on Form 10-Q filed with the Securities and Exchange Commission on December 10, 2025, (ii) 2,227,542 shares of Class B common stock (such shares treated as converted into shares of Class A common stock solely for the purposes of computing the percentage of ownership of the Reporting Person pursuant to Rule 13d-3 of the Securities Exchange Act of 1934, as amended), and (iii) 779,319 shares of Class A common stock underlying stock options exercisable within 60 days of the date of this Statement held by the Reporting Person.

SCHEDULE 13G

Item 1.

(a)

Name of issuer:

BillionToOne, Inc.

(b)

Address of issuer's principal executive offices:

1035 O'Brien Drive, Menlo Park, CA 94025

Item 2.

(a)

Name of person filing:

Oguzhan Atay

(b)

Address or principal business office or, if none, residence:

The address of the principal business office of the Reporting Person is 1035 O'Brien Drive, Menlo Park, CA 94025.

(c)

Citizenship:

The Reporting Person is a citizen of the United States of America.

(d)

Title of class of securities:

Class A common stock, par value $0.00001 per share

(e)

CUSIP No.:

090168105

Item 3.

If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

(a)

Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);

(b)

Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);

(c)

Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);

(d)

Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);

(e)

An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);

(f)

An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);

(g)

A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);

(h)

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j)

A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:

(k)

Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).

Item 4.

Ownership

(a)

Amount beneficially owned:

See Row 9 of the cover page for the Reporting Person and the corresponding comments.

(b)

Percent of class:

See Row 11 of the cover page for the Reporting Person and the corresponding comments.

(c)

Number of shares as to which the person has:

(i) Sole power to vote or to direct the vote:

See Row 5 of the cover page for the Reporting Person and the corresponding comments.

(ii) Shared power to vote or to direct the vote:

See Row 6 of the cover page for the Reporting Person and the corresponding comments.

(iii) Sole power to dispose or to direct the disposition of:

See Row 7 of the cover page for the Reporting Person and the corresponding comments.

(iv) Shared power to dispose or to direct the disposition of:

See Row 8 of the cover page for the Reporting Person and the corresponding comments.

Item 5.

Ownership of 5 Percent or Less of a Class.

Not Applicable

Item 6.

Ownership of more than 5 Percent on Behalf of Another Person.

Not Applicable

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.

Not Applicable

Item 8.

Identification and Classification of Members of the Group.

Not Applicable

Item 9.

Notice of Dissolution of Group.

Not Applicable

Item 10.

Certifications:

Not Applicable

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Oguzhan Atay

Signature:	/s/ Thomas Lynch, Attorney-in-fact
Name/Title:	Thomas Lynch, Attorney-in-fact
Date:	02/17/2026

SEC Form SCHEDULE 13G filed by BillionToOne Inc.