Company: BLLN
Filing Date: 2025-10-07
Form Type: S-1
Source: 0001193125-25-233697
Chunk: 33

Company: BillionToOne, Inc.
Filing Date: 2025-10-07
Form: S-1
Chunk 33
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 longer serving as an officer or director of the Company. See the section titled “Description of capital stock—Common stock.”         |

| Directed share program | At our request, the underwriters have reserved up to 5% of the shares of Class A common stock being offered by this prospectus for sale, at the initial                                                                                             
 public offering price, to our officers, directors and employees through a directed share program. Shares purchased through the directed share program will not be subject to a lock-up restriction,                                                 
 except in the case of shares purchased by any of our directors or officers. We do not know if these parties will choose to purchase all or any portion of these reserved shares, but the number of shares of our Class A common stock available for 
 sale to the general public will be reduced to the extent these individuals or entities purchase such reserved shares. Any reserved shares that are not so purchased will be offered by the underwriters to the                                      |

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| general public on the same terms as the other shares offered by this prospectus. J.P. Morgan Securities LLC will administer our directed share program. See the section titled 
 “Underwriting–Directed share program” for additional information.                                                                                                              |

| Risk factors | See the section titled “Risk factors” for a discussion of factors that you should consider carefully before deciding to invest in our Class A common stock. |

| Proposed Nasdaq Global Select Market trading symbol | “BLLN” |

The number of shares of our common stock to be outstanding after this offering is based on 35,616,629 shares of our Class A common stock and 4,552,650 shares of our Class B common stock outstanding as of June 30, 2025, after giving effect to the Preferred Stock Conversion, the Reclassification and the Class B Stock Exchange (each as defined below), in each case as if they had occurred on June 30, 2025, and excludes:

| • |     | 8,930,919 shares of our Class A common stock issuable upon the exercise of stock options outstanding as of                     
 June 30, 2025 under our 2018 Stock Plan, as amended (the 2018 Plan), at a weighted-average exercise price of $10.59 per share; |

| • |     | 1,224,549 shares of our Class 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