# EDGAR Filing Document

**Accession Number:** 0002070849
**File Stem:** 0001193125-26-055007
**Filing Date:** 2026-2
**Character Count:** 8513
**Document Hash:** 3a3f81128c6da131be45dc2763fb574f
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-26-055007.hdr.sgml**: 20260217

**ACCESSION NUMBER**: 0001193125-26-055007

**CONFORMED SUBMISSION TYPE**: SCHEDULE 13G

**PUBLIC DOCUMENT COUNT**: 1

**FILED AS OF DATE**: 20260217

**DATE AS OF CHANGE**: 20260217

**SUBJECT COMPANY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** BillionToOne, Inc.
- **CENTRAL INDEX KEY:** 0002070849
- **STANDARD INDUSTRIAL CLASSIFICATION:** SERVICES-MEDICAL LABORATORIES [8071]
- **ORGANIZATION NAME:** 08 Industrial Applications and Services
- **EIN:** 811082020
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13G
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-95426
- **FILM NUMBER:** 26643218

**BUSINESS ADDRESS:**
- **STREET 1:** 1035 O'BRIEN DRIVE
- **CITY:** MENLO PARK
- **STATE:** CA
- **BUSINESS PHONE:** 650-460-2551

**MAIL ADDRESS:**
- **STREET 1:** 1035 O'BRIEN DRIVE
- **CITY:** MENLO PARK
- **STATE:** CA
- **ZIP:** 94025
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Tsao David
- **CENTRAL INDEX KEY:** 0002087127

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13G

**MAIL ADDRESS:**
- **STREET 1:** 1035 O'BRIEN DRIVE
- **CITY:** MENLO PARK
- **STATE:** CA
- **ZIP:** 94025

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

## SCHEDULE 13G

### Under the Securities Exchange Act of 1934

**Issuer:** BillionToOne, Inc.

**Title of Class of Securities:** Class A common stock, par value $0.00001 per share

**CUSIP Number:** 090168105

**Date of Event Which Requires Filing of this Statement:** 12/31/2025

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

- [ ] Rule 13d-1(b)

- [ ] Rule 13d-1(c)

- [x] Rule 13d-1(d)

---

| 1. | Names of Reporting Persons<br>David Tsao | Names of Reporting Persons<br>David Tsao |
|:---|:---|:---|:---|
| 2. | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [ ] | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [ ] |
| 3. | SEC Use Only | SEC Use Only |
| 4. | Citizenship or Place of Organization<br>X1 | Citizenship or Place of Organization<br>X1 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 5. | Sole Voting Power<br>3035767 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 6. | Shared Voting Power<br>0 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 7. | Sole Dispositive Power<br>3035767 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 8. | Shared Dispositive Power<br>0 |
| 9. | Aggregate Amount Beneficially Owned by Each Reporting Person<br>3035767 | Aggregate Amount Beneficially Owned by Each Reporting Person<br>3035767 |
| 10. | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] |
| 11. | Percent of Class Represented by Amount in Row (9)<br>6.9% | Percent of Class Represented by Amount in Row (9)<br>6.9% |
| 12. | Type of Reporting Person (See Instructions)<br>IN | Type of Reporting Person (See Instructions)<br>IN |

**Comment for Type of Reporting Person:** Consists of (i) 1,000 shares of Class A common stock of the Issuer (as defined in item 1(a) below), (ii) 2,325,108 shares of Class B common stock of the Issuer, and (iii) 709,659 shares of Class A common stock underlying stock options exercisable within 60 days of the date of this Statement held by David Tsao (the Reporting Person). Each share of Class B common stock is convertible into one share of Class A common stock at the option of the holder. Excludes 431,892 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 44,250,877 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) 2,325,108 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) 709,659 shares of Class A common stock underlying stock options exercisable within 60 days of the date of this Statement held by the Reporting Person.

---

**Item 1(a). Name of Issuer:**
BillionToOne, Inc.

**Item 1(b). Address of Issuer's Principal Executive Offices:**
1035 O'Brien Drive, Menlo Park, CA 94025

**Item 2(a). Name of Person Filing:**
David Tsao

**Item 2(b). Address of Principal Business Office:**
The address of the principal business office of the Reporting Person is 1035 O'Brien Drive, Menlo Park, CA 94025.

**Item 2(c). Citizenship:**
The Reporting Person is a citizen of the United States of America.

**Item 2(d). Title of Class of Securities:**
Class A common stock, par value $0.00001 per share

**Item 2(e). CUSIP Number:**
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 Five Percent or Less of a Class.**

[x] If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following.

**Item 6. Ownership of More than 5 Percent on Behalf of Another Person.**

Not Applicable

**Item 7. Identification and Classification of the Subsidiary**

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. Certification:**

—

### 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.

**David Tsao**

**Date:** 02/17/2026

**By:** /s/ Thomas Lynch, Attorney-in-fact

**Name & Title:** Thomas Lynch, Attorney-in-fact