Company: BLLN
Filing Date: 2025-06-20
Form Type: DRS
Source: 0000950123-25-006095
Chunk: 20

Company: BillionToOne, Inc.
Filing Date: 2025-06-20
Form: DRS
Chunk 20
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 June 30, 2025, and excludes:

| • |     | up to 9,660 shares of our Class A common stock issuable upon the exercise of a redeemable convertible preferred stock 
 warrant (the A-6 Warrant) for an exercise price of $2.5879 per share;                                                 |

| • |     | up to 80,357 shares of our Class A common stock issuable upon the exercise of a 2021 common stock warrant (the 2021 
 Common Warrant) for an exercise price of $2.80 per share;                                                           |

| • |     | up to 41,209 shares of our Class A common stock issuable upon the exercise of a 2022 common stock warrant (the 2022 
 Common Warrant) for an exercise price of $10.92 per share;                                                          |

| • |     | shares of our Class A common stock reserved for future issuance under our 2025 Equity Incentive                                                                                                                                                
 Plan (the 2025 Plan), which will become effective upon the effectiveness of the registration statement of which this prospectus forms a part, as well as any future increases in the number of shares of our Class A common stock reserved for 
 issuance under the 2025 Plan; and                                                                                                                                                                                                              |

| • |     | shares of our Class A common stock reserved for future issuance under our 2025 Employee Stock                                                                                                                                                  
 Purchase Plan (ESPP), which will become effective upon the effectiveness of the registration statement of which this prospectus forms a part, as well as any future increases in the number of shares of our Class A common stock reserved for 
 issuance under the ESPP.                                                                                                                                                                                                                       |

Unless otherwise indicated, this prospectus reflects and assumes the following:

| • |     | the automatic conversion of all    outstanding shares of our redeemable convertible preferred stock into                            
 an aggregate of   shares of our common stock immediately prior to the completion of this offering (the Preferred Stock Conversion); |

| • |     | the automatic adjustment of the A-6 Warrant into a warrant to purchase 9,660 shares 
 of our common stock immediately prior to the completion of this offering;           |

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| • |     | the filing and effectiveness of our Post-IPO Certificate of Incorporation                                                                                                                                                                          
 immediately prior to the completion of this offering, which, among other things, will reclassify all outstanding shares of our common stock into an equal number of shares of Class A