# EDGAR Filing Document

**Accession Number:** 0002070849
**File Stem:** 0001104659-26-005176
**Filing Date:** 2026-1
**Character Count:** 29194
**Document Hash:** e2e920e5d65abd09e85c3f9369ae8757
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001104659-26-005176.hdr.sgml**: 20260120

**ACCESSION NUMBER**: 0001104659-26-005176

**CONFORMED SUBMISSION TYPE**: SCHEDULE 13D

**PUBLIC DOCUMENT COUNT**: 1

**FILED AS OF DATE**: 20260120

**DATE AS OF CHANGE**: 20260120

**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 13D
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-95426
- **FILM NUMBER:** 26544399

**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:** Humming Bird Ventures Management NV
- **CENTRAL INDEX KEY:** 0002099044

**ORGANIZATION NAME:**
- **EIN:** 000000000
- **STATE OF INCORPORATION:** C9
- **FISCAL YEAR END:** 1231

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

**BUSINESS ADDRESS:**
- **ADDRESS IS A NON US LOCATION:** YES
- **STREET 1:** SQUARE VICTORIA REGINA 1
- **CITY:** SINT-JOOST-TEN-NODE
- **PROVINCE COUNTRY:** C9
- **ZIP:** 1210
- **BUSINESS PHONE:** 0032477 58 95 42

**MAIL ADDRESS:**
- **ADDRESS IS A NON US LOCATION:** YES
- **STREET 1:** SQUARE VICTORIA REGINA 1
- **CITY:** SINT-JOOST-TEN-NODE
- **PROVINCE COUNTRY:** C9
- **ZIP:** 1210

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

## SCHEDULE 13D

### Under the Securities Exchange Act of 1934

**BillionToOne**

*(Name of Issuer)*

**Class A common stock**

*(Title of Class of Securities)*

**090168105**

*(CUSIP Number)*

**Lucas De Four**<br>Square Victoria Regina 1<br>Sint-Joost-ten-Node C9 1210<br>0032477 58 95 42

*(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)*

**11/06/2025**

*(Date of Event Which Requires Filing of this Statement)*

| **CUSIP No.** | **090168105** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Hummingbird Ventures Management NV** | Name of reporting person<br>**Hummingbird Ventures Management NV** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**C9** | Citizenship or place of organization<br>**C9** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**7887237.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**7887237.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**7887237.00** | Aggregate amount beneficially owned by each reporting person<br>**7887237.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**19.6%** | Percent of class represented by amount in Row (11)<br>**19.6%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**CO** | Type of Reporting Person (See Instructions)<br>**CO** | |

---

**Comment for Reporting Person:** For item 13: This calculation is based upon 40,167,729 Class A common stock shares outstanding as of November 6, 2025, as disclosed on the Issuer's initial public offering (the "IPO") prospectus filed with the Securities and Exchange Commission on November 6, 2025.

| **CUSIP No.** | **090168105** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Hummingbird Opportunity Fund II CommV** | Name of reporting person<br>**Hummingbird Opportunity Fund II CommV** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**WC** | Source of funds (See Instructions)<br>**WC** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**C9** | Citizenship or place of organization<br>**C9** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2631664.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2631664.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2631664.00** | Aggregate amount beneficially owned by each reporting person<br>**2631664.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**6.55%** | Percent of class represented by amount in Row (11)<br>**6.55%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**PN** | Type of Reporting Person (See Instructions)<br>**PN** | |

---

**Comment for Reporting Person:** For item 13: This calculation is based upon 40,167,729 Class A common stock shares outstanding as of November 6, 2025, as disclosed on the Issuer's IPO prospectus filed with the Securities and Exchange Commission on November 6, 2025.

| **CUSIP No.** | **090168105** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Hummingbird Ventures III CommV** | Name of reporting person<br>**Hummingbird Ventures III CommV** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**WC** | Source of funds (See Instructions)<br>**WC** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**C9** | Citizenship or place of organization<br>**C9** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2580833.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2580833.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2580833.00** | Aggregate amount beneficially owned by each reporting person<br>**2580833.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**6.43%** | Percent of class represented by amount in Row (11)<br>**6.43%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**PN** | Type of Reporting Person (See Instructions)<br>**PN** | |

---

**Comment for Reporting Person:** For item 13: This calculation is based upon 40,167,729 Class A common stock shares outstanding as of November 6, 2025, as disclosed on the Issuer's IPO prospectus filed with the Securities and Exchange Commission on November 6, 2025.

| **CUSIP No.** | **090168105** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Hummingbird Dragons CommV** | Name of reporting person<br>**Hummingbird Dragons CommV** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**WC** | Source of funds (See Instructions)<br>**WC** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**C9** | Citizenship or place of organization<br>**C9** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**2015118.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**2015118.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**2015118.00** | Aggregate amount beneficially owned by each reporting person<br>**2015118.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**5.02%** | Percent of class represented by amount in Row (11)<br>**5.02%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**PN** | Type of Reporting Person (See Instructions)<br>**PN** | |

---

**Comment for Reporting Person:** For item 13: This calculation is based upon 40,167,729 Class A common stock shares outstanding as of November 6, 2025, as disclosed on the Issuer's IPO prospectus filed with the Securities and Exchange Commission on November 6, 2025.

| **CUSIP No.** | **090168105** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Hummingbird Collective CommV** | Name of reporting person<br>**Hummingbird Collective CommV** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**WC** | Source of funds (See Instructions)<br>**WC** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**C9** | Citizenship or place of organization<br>**C9** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**18845.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**18845.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**18845.00** | Aggregate amount beneficially owned by each reporting person<br>**18845.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**0.05%** | Percent of class represented by amount in Row (11)<br>**0.05%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**PN** | Type of Reporting Person (See Instructions)<br>**PN** | |

---

**Comment for Reporting Person:** For item 13: This calculation is based upon 40,167,729 Class A common stock shares outstanding as of November 6, 2025, as disclosed on the Issuer's IPO prospectus filed with the Securities and Exchange Commission on November 6, 2025.

| **CUSIP No.** | **090168105** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**HB&Q NV** | Name of reporting person<br>**HB&Q NV** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**WC** | Source of funds (See Instructions)<br>**WC** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**C9** | Citizenship or place of organization<br>**C9** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**640727.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**640727.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**640727.00** | Aggregate amount beneficially owned by each reporting person<br>**640727.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**1.60%** | Percent of class represented by amount in Row (11)<br>**1.60%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**CO** | Type of Reporting Person (See Instructions)<br>**CO** | |

---

**Comment for Reporting Person:** For item 13: This calculation is based upon 40,167,729 Class A common stock shares outstanding as of November 6, 2025, as disclosed on the Issuer's IPO prospectus filed with the Securities and Exchange Commission on November 6, 2025.

| **CUSIP No.** | **090168105** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Firat Ileri** | Name of reporting person<br>**Firat Ileri** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**G4** | Citizenship or place of organization<br>**G4** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**7887237.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**7887237.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**7887237.00** | Aggregate amount beneficially owned by each reporting person<br>**7887237.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**19.6%** | Percent of class represented by amount in Row (11)<br>**19.6%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

**Comment for Reporting Person:** For item 13: This calculation is based upon 40,167,729 Class A common stock shares outstanding as of November 6, 2025, as disclosed on the Issuer's IPO prospectus filed with the Securities and Exchange Commission on November 6, 2025.

| **CUSIP No.** | **090168105** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Barend Van den Brande** | Name of reporting person<br>**Barend Van den Brande** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**C9** | Citizenship or place of organization<br>**C9** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**7887237.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**7887237.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**7887237.00** | Aggregate amount beneficially owned by each reporting person<br>**7887237.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**19.6%** | Percent of class represented by amount in Row (11)<br>**19.6%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

**Comment for Reporting Person:** For item 13: This calculation is based upon 40,167,729 Class A common stock shares outstanding as of November 6, 2025, as disclosed on the Issuer's IPO prospectus filed with the Securities and Exchange Commission on November 6, 2025.

| **CUSIP No.** | **090168105** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Lukas Decoster** | Name of reporting person<br>**Lukas Decoster** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[ ] (a)<br>[x] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**C9** | Citizenship or place of organization<br>**C9** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**7887237.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**7887237.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**7887237.00** | Aggregate amount beneficially owned by each reporting person<br>**7887237.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**19.6%** | Percent of class represented by amount in Row (11)<br>**19.6%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

**Comment for Reporting Person:** For item 13: This calculation is based upon 40,167,729 Class A common stock shares outstanding as of November 6, 2025, as disclosed on the Issuer's IPO prospectus filed with the Securities and Exchange Commission on November 6, 2025.

**Item 1. Security and Issuer**

**(a) Title of Class of Securities:**
Class A common stock

**(b) Name of Issuer:**
BillionToOne

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

This Schedule 13D relates to the Class A common stock of BilliontoOne, Inc., a Delaware corporation (the "Issuer"). The principal executive offices of the Issuer are located at 1035 O'Brien Drive, Menlo Park, CA 94025.

**Item 4. Purpose of Transaction**

The Shares reported herein as being beneficially owned by the Reporting Persons were acquired for investment purposes.

The Reporting Persons acquired beneficial ownership of the shares as described in this Schedule 13D for investment purposes and intend to review their investment in the Issuer on a continuing basis. Depending on various factors, including but not limited to the Issuer's business, prospects, financial position and strategic direction, price levels of the shares, conditions in the securities markets, and general economic and industry conditions, each Reporting Person may in the future take such actions with respect to its investment in the Issuer as it deems appropriate, including changing its current intentions, with respect to any or all matters required to be disclosed in this Schedule 13D.

Fiat Ileri is a director of the Issuer. Consistent with the Reporting Persons' investment purposes, the Reporting Persons may engage in communications with, without limitation, one or more shareholders of the Issuer, management of the Issuer or one or more members of the board of directors of the Issuer, and may make suggestions concerning the Issuer's operations, prospects, business and financial strategies, strategic direction and transactions, assets and liabilities, business and financing alternatives and such other matters as the Reporting Persons may deem relevant to their investment in the Issuer. The Reporting Persons expect that they will, from time to time, review their investment position in the Issuer and may make additional purchases of Class A common stock of the Issuer (or other securities convertible or exercisable into Class A common stock) in the open market or in privately negotiated transactions, or hold or dispose of all or part of their investments in the shares, depending upon the Reporting Persons' evaluation of the Issuer's business, prospects, financial condition and strategic direction, the market for the shares, other opportunities available to the Reporting Persons, general economic conditions, stock market conditions and other factors.

Except as set forth in this Item 4 or Item 6 below, the Reporting Persons have no present plans or proposals that relate to or that would result in any of the actions specified in clauses (a) through (j) of Item 4 of Schedule 13D of the Act.

**Item 5. Interest in Securities of the Issuer**

**(a)**
The information contained in rows 7, 8, 9, 10, 11 and 13 on each of the cover pages of this Schedule 13D is incorporated by reference in its entirety into this Item 5.

Pursuant to Rule 13d-3 under the Act, each of the Reporting Persons may be deemed to beneficially own and share voting and dispositive power in respect of 40,167,729 Shares.

This calculation is based upon 40,167,729 Class A common stock shares outstanding as of September 30, 2025, as disclosed on the Issuer's IPO prospectus filed with the Securities and Exchange Commission on November 6, 2025.

**(b)**
N/A

**(c)**
To the knowledge of the Reporting Persons, no person other than the Reporting Persons is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of the Shares beneficially owned by the Reporting Persons identified in this Item 5.

**Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.**

None

### 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.

**Reporting Person:** Hummingbird Ventures Management NV

**Signature:** /s/ Lukas Decoster

**Name/Title:** 49/9 CommV, represented by its permanent representative Lukas Decoster, Director

**Date:** 01/20/2026

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.

**Reporting Person:** Hummingbird Opportunity Fund II CommV

**Signature:** /s/ Firat Ileri

**Name/Title:** Hummingbird Ventures Management NV, its Manager; Firat Ileri, Permanent Representative

**Date:** 01/20/2026

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.

**Reporting Person:** Hummingbird Ventures III CommV

**Signature:** /s/ Firat Ileri

**Name/Title:** Hummingbird Ventures Management NV, its Manager; Firat Ileri, Permanent Representative

**Date:** 01/20/2026

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.

**Reporting Person:** Hummingbird Dragons CommV

**Signature:** /s/ Firat Ileri

**Name/Title:** Hummingbird Ventures Management NV, its Manager; Firat Ileri, Permanent Representative

**Date:** 01/20/2026

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.

**Reporting Person:** Hummingbird Collective CommV

**Signature:** /s/ Firat Ileri

**Name/Title:** Hummingbird Ventures Management NV, its Manager; Firat Ileri, Permanent Representative

**Date:** 01/20/2026

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.

**Reporting Person:** HB&Q NV

**Signature:** /s/ Firat Ileri

**Name/Title:** Hummingbird Ventures Management NV, its Manager; Firat Ileri, Permanent Representative

**Date:** 01/20/2026

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.

**Reporting Person:** Firat Ileri

**Signature:** /s/ Firat Ileri

**Name/Title:** Firat Ileri

**Date:** 01/20/2026

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.

**Reporting Person:** Barend Van den Brande

**Signature:** /s/ Barend Van den Brande

**Name/Title:** Barend Van den Brande

**Date:** 01/20/2026

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.

**Reporting Person:** Lukas Decoster

**Signature:** /s/ Lukas Decoster

**Name/Title:** Lukas Decoster

**Date:** 01/20/2026