Company: BLLN
Filing Date: 2025-10-17
Form Type: S-1/A
Source: 0001193125-25-242632
Chunk: 309

Company: BillionToOne, Inc.
Filing Date: 2025-10-17
Form: S-1/A
Chunk 309
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 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 Class A common stock then outstanding, which will equal 394,626 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 with respect to such sale.                                                                                      |

Sales under Rule 144 by our affiliates or persons selling shares on behalf of our affiliates are also subject to certain manner of sale provisions and notice requirements and to the availability of current public information about us. Rule 701 Rule 701 under the Securities Act, or Rule 701, generally allows a stockholder who was issued shares under a written compensatory plan or contract and who is not deemed to have been an affiliate of our company during the immediately preceding 90 days, to sell these shares in reliance on Rule 144, but without being required to comply with the public information, holding period, manner of sale limitations, volume limitation, or notice provisions of Rule 144. Rule 701 also permits affiliates of our company to sell their Rule 701 shares under Rule 144 without complying with the holding period requirements of Rule 144. All holders of Rule 701 shares, however, are required by that rule to wait until 90 days after the date of this prospectus before selling those shares under Rule 701, subject to the expiration of the lock-upagreements and market stand-offarrangements described below. Form S-8registration statements We intend to file one or more registration statements on Form S-8under the Securities Act with the SEC as soon as practicable after the time at which the registration statement of which this prospectus forms a part becomes effective to register the offer and sale of shares of our Class A common stock that are subject to outstanding stock options and Class A common stock issued or issuable under our employee benefit plans as defined in Form S-8.These registration