Company: BLLN
Filing Date: 2025-10-17
Form Type: S-1/A
Source: 0001193125-25-242632
Chunk: 283

Company: BillionToOne, Inc.
Filing Date: 2025-10-17
Form: S-1/A
Chunk 283
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 of the 2018 Plan, which is filed as an exhibit to the registration statement of which this prospectus is a part. To the extent there is a conflict between the terms of this summary and the 2018 Plan, the terms of the 2018 Plan will control. Types of awards The 2018 Plan provides for the grant of incentive stock options, or ISOs, nonstatutory stock options, or NSOs, and awards of restricted stock (collectively, stock awards). ISOs may be granted only to our employees, but not employees of our affiliates. All other awards may be granted to our employees, our non-employeedirectors and consultants and the employees and consultants of our affiliates. Share reserve As of June 30, 2025, we have reserved 12,409,025 shares of our common stock for issuance under the 2018 Plan, all of which may be issued as incentive stock options. Unissued shares subject to awards that expire or 209

become unexercisable without being exercised in full or are surrendered pursuant to an option exchange program and shares that are forfeited, cancelled, reacquired by us or withheld in payment of the purchase price or exercise price of an award or in satisfaction of withholding taxes will again become available for issuance under the 2025 Plan. Administration Our Board of Directors, or a committee thereof, has administered the 2018 Plan since its adoption; however, following this offering, the compensation committee of our Board of Directors will generally administer the 2018 Plan. The administrator has complete discretion to make all decisions relating to the 2018 Plan and outstanding awards. Eligibility Our employees, non-employee membersof our Board of Directors and consultants, including those of our affiliates, are eligible to participate in the 2018 Plan. However, only our direct employees are eligible to receive incentive stock options. Options The exercise price for options granted under the 2018 Plan is determined by the administrator, but, in the case of ISOs, may not be less than 100% of the fair market value of our common stock on the grant date. Optionees may pay the exercise price in cash or cash equivalents or by one, or any combination of, the following forms of payment, as permitted by the administrator in its sole discretion:

| • |     | Delivery of a promissory note, with the recourse, interest, security and redemption provisions determined by the 
 administrator to the extent permitted under and in accordance with applicable law;                               |