Company: BLLN
Filing Date: 2025-06-20
Form Type: DRS
Source: 0000950123-25-006095
Chunk: 252

Company: BillionToOne, Inc.
Filing Date: 2025-06-20
Form: DRS
Chunk 252
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 to the volume, manner of sale, and other restrictions of Rule 144, as described below.                                                                         |

In addition, after this offering, up to shares of Class A common stock may be issued upon exercise of outstanding stock options as of June 30, 2025, and shares of Class A common stock are available for future issuance under our 2018 Plan. Rule 144 In general, under Rule 144 as currently in effect, once we have been subject to public company reporting requirements of Section 13 or Section 15(d) of the Exchange Act for at least 90 days, an eligible stockholder is entitled to sell such shares without complying with the manner of sale, volume limitation, or notice provisions of Rule 144, subject to compliance with the public information requirements of Rule 144. To be an eligible stockholder under Rule 144, such stockholder must not be deemed to have been one of our affiliates for purposes of the Securities Act at any time during the 90 days preceding a sale and must have beneficially 200

owned the shares proposed to be sold for at least six months, including the holding period of any prior owner other than our affiliates. If such a person has beneficially owned the shares proposed to be sold for at least one year, including the holding period of any prior owner other than our affiliates, then such person is entitled to sell such shares without complying with any of the requirements of Rule 144, subject to the expiration of the lock-upagreements and/or market stand-offarrangements described below, which prevent the sale of shares. In general, under Rule 144, as currently in effect, our affiliates or persons selling shares on behalf of our affiliates are entitled to sell shares on expiration of the lock-upagreements and/or market standoff arrangements described below, subject, in the case of restricted securities, to such shares having been beneficially owned for at least six months. Beginning 90 days after the date of this prospectus, within any three-month period, such stockholders may sell a number of shares that does not exceed the greater of:

| • |     | 1% of the number of shares of common stock then outstanding, which will equal    shares immediately                             
 after this offering, assuming no exercise of the underwriters’ option to purchase additional shares of common stock from us; or |

| • |     | the average weekly trading volume of our common stock during the four calendar weeks preceding the filing of a notice on 
 Form 144