Company: BLLN
Filing Date: 2025-10-17
Form Type: S-1/A
Source: 0001193125-25-242632
Chunk: 35

Company: BillionToOne, Inc.
Filing Date: 2025-10-17
Form: S-1/A
Chunk 35
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 A common stock issuable upon the exercise of outstanding stock options that were granted 
 subsequent to June 30, 2025 under our 2018 Plan, at a weighted-average exercise price of $28.88 per share;             |

| • |     | 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;                                                          |

| • |     | 3,255,666 shares of our Class A common stock reserved for future issuance under our 2025 Equity Incentive Plan                                                                                                                                          
 (the 2025 Plan), based on an assumed offering size of 3,846,000 shares of Class A common stock, 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                                                                                                                                                      |

| • |     | 542,316 shares of our Class A common stock reserved for future issuance under our 2025 Employee Stock Purchase                                                                                                                                         
 Plan (ESPP), based on an assumed offering size of 3,846,000 shares of Class A common stock, 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.                                                                                                                                                                 |

17

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

| • |     | the automatic conversion of all 29,084,235 outstanding shares of our redeemable convertible preferred stock into an                       
 aggregate of 29,084,235 shares of our common stock immediately prior to the completion of this offering (the Preferred Stock Conversion); |

| • |     | the automatic adjustment of the A