Company: BLLN
Filing Date: 2025-09-17
Form Type: DRS/A
Source: 0001193125-25-206347
Chunk: 305

Company: BillionToOne, Inc.
Filing Date: 2025-09-17
Form: DRS/A
Chunk 305
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Rule 10b5-1plans

After this
offering, certain of our employees, including our executive officers, and/or directors may enter into written trading plans that are intended to comply with Rule 10b5-1 under the Exchange Act. Sales under
these trading plans would not be permitted until the expiration of the lock-up agreements or market stand-off arrangements relating to the offering described above.

226

Material U.S. federal income tax consequences to non-U.S.holders of our Class A common stock The following is a general discussion of the material U.S. federal income tax considerations applicable to non-U.S.holders (as defined below) with respect to their ownership and disposition of shares of our Class A common stock issued pursuant to this offering. All prospective non-U.S.holders of our Class A common stock should consult their tax advisors with respect to the U.S. federal, state, local and non-U.S.tax consequences of the purchase, ownership and disposition of our Class A common stock. For purposes of this discussion, a non-U.S.holder means a beneficial owner of our Class A common stock (other than an entity or arrangement that is treated as a partnership or pass-through entity for U.S. federal income tax purposes) that is not, for U.S. federal income tax purposes, any of the following:

| • |     | an individual citizen or resident of the United States; |

| • |     | a corporation (or other entity treated as a corporation for U.S. federal income tax purposes) created or organized in the 
 United States or under the laws of the United States, any state thereof or the District of Columbia;                      |

| • |     | an estate, the income of which is includable in gross income for U.S. federal income tax purposes regardless of its source; 
 or                                                                                                                          |

| • |     | a trust if (1) a court within the United States is able to exercise primary supervision over the administration of the                                                                                                                  
 trust and one or more “U.S. persons,” as defined under the Code (as defined below), have the authority to control all substantial decisions of the trust or (2) such trust has made a valid election to be treated as a U.S. person for 
 U.S. federal income tax purposes.                                                                                                                                                                                                       |

This discussion is based on current provisions of the Internal Revenue Code of 1986, as amended (the Code), existing, temporary and proposed U.S. treasury regulations promulgated thereunder (Treasury Regulations),