# EDGAR Filing Document

**Accession Number:** 0002070849
**File Stem:** 0002087127-26-000002
**Filing Date:** 2026-6
**Character Count:** 11233
**Document Hash:** 04adaa9421cd4988843d9ffe840084db
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0002087127-26-000002.hdr.sgml**: 20260617

**ACCESSION NUMBER**: 0002087127-26-000002

**CONFORMED SUBMISSION TYPE**: 4

**PUBLIC DOCUMENT COUNT**: 1

**CONFORMED PERIOD OF REPORT**: 20260615

**FILED AS OF DATE**: 20260617

**DATE AS OF CHANGE**: 20260617

**REPORTING-OWNER**: 

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

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** 4
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-42934
- **FILM NUMBER:** 261099624

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

**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

**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

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

## FORM 4

### STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

[ ] Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

[x] Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

---

| | | |
|:---|:---|:---|
| **1. Name and Address of Reporting Person**<sup>*</sup><br>Tsao David<br><sub>(Last) (First) (Middle)</sub><br>C/O BILLIONTOONE, INC.<br>1035 O'BRIEN DRIVE<br><sub>(Street)</sub><br>MENLO PARK, CA 94025<br><sub>(City) (State) (Zip)</sub> | **3. Date of Earliest Transaction (Month/Day/Year)**<br>2026-06-15 | **5. Relationship of Reporting Person(s) to Issuer**<br>(Check all applicable)<br>[X] Director [ ] 10% Owner<br>[X] Officer (give title below) [ ] Other (specify below)<br>_Chief Technology Officer_ |
| **2. Issuer Name and Ticker or Trading Symbol**<br>BillionToOne, Inc. [ BLLN ] | **4. If Amendment, Date of Original Filed (Month/Day/Year)**<br>  | **6. Individual or Joint/Group Filing (Check Applicable Line)**<br>[X] Form filed by One Reporting Person<br>[ ] Form filed by More than One Reporting Person |

---

## Table I - Non-Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | 3. Transaction Code (V) | 3. Transaction Code (V) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | Code | V | Amount | (A) or (D) | Price | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
| Class A Common Stock | 2026-06-15 |  | M<sup>(1)</sup> |  | 10000 | A | $2.80 | 11000 | D |  |
| Class A Common Stock | 2026-06-15 |  | M<sup>(1)</sup> |  | 10000 | A | $2.80 | 21000 | D |  |
| Class A Common Stock | 2026-06-15 |  | S<sup>(1)</sup> |  | 1704 | D | 100.3718<sup>(2)</sup> | 19296 | D |  |
| Class A Common Stock | 2026-06-15 |  | S<sup>(1)</sup> |  | 2361 | D | 101.5524<sup>(3)</sup> | 16935 | D |  |
| Class A Common Stock | 2026-06-15 |  | S<sup>(1)</sup> |  | 2816 | D | 102.7739<sup>(4)</sup> | 14119 | D |  |
| Class A Common Stock | 2026-06-15 |  | S<sup>(1)</sup> |  | 2889 | D | 103.6843<sup>(5)</sup> | 11230 | D |  |
| Class A Common Stock | 2026-06-15 |  | S<sup>(1)</sup> |  | 230 | D | 104.472<sup>(6)</sup> | 11000 | D |  |
| Class A Common Stock | 2026-06-15 |  | S<sup>(1)</sup> |  | 600 | D | 98.7417<sup>(7)</sup> | 10400 | D |  |
| Class A Common Stock | 2026-06-15 |  | S<sup>(1)</sup> |  | 1000 | D | 100.053<sup>(8)</sup> | 9400 | D |  |
| Class A Common Stock | 2026-06-15 |  | S<sup>(1)</sup> |  | 2461 | D | 101.3707<sup>(9)</sup> | 6939 | D |  |
| Class A Common Stock | 2026-06-15 |  | S<sup>(1)</sup> |  | 2978 | D | 102.5988<sup>(10)</sup> | 3961 | D |  |
| Class A Common Stock | 2026-06-15 |  | S<sup>(1)</sup> |  | 2398 | D | 103.6289<sup>(11)</sup> | 1563 | D |  |
| Class A Common Stock | 2026-06-15 |  | S<sup>(1)</sup> |  | 563 | D | 104.3167<sup>(12)</sup> | 1000 | D |  |

---

## Table II - Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | 4. Transaction Code (V) | 4. Transaction Code (V) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 6. Date Exercisable and Expiration Date | 6. Date Exercisable and Expiration Date | 7. Title and Amount of Underlying Securities | 7. Title and Amount of Underlying Securities | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | Code | V | (A) | (D) | Date Exercisable | Expiration Date | Title | Amount or Number of Shares | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| Stock Option (right to buy) | $2.80 | 2026-06-15 |  | M |  |  | 10000 | <sup>(13)</sup> | 2031-06-07 | Class A Common Stock | 10000 | $2.80 | 630000 | D |  |
| Stock Option (right to buy) | $2.80 | 2026-06-15 |  | M |  |  | 10000 | <sup>(13)</sup> | 2031-06-07 | Class A Common Stock | 10000 | $2.80 | 620000 | D |  |

---

### Footnotes:

(1) The transactions reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on March 6, 2026.

(2) The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $100.000 to $100.9175 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

(3) The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $101.120 to $102.020 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

(4) The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $102.185 to $103.150 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

(5) The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $103.250 to $104.200 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

(6) The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $104.360 to $104.610 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

(7) The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $98.160 to $99.080 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

(8) The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $99.840 to $100.280 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

(9) The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $100.860 to $101.800 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

(10) The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $101.980 to $102.970 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

(11) The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $103.140 to $104.130 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

(12) The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $104.160 to $104.540 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

(13) The options are fully vested and exercisable.

**Signature:** /s/ Thomas P. Lynch, Attorney-in-Fact  
**Date:** 2026-06-17

### Remarks:

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* 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).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.

**Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.**