Company: BLLN
Filing Date: 2025-08-11
Form Type: DRS/A
Source: 0000950123-25-007483
Chunk: 260

Company: BillionToOne, Inc.
Filing Date: 2025-08-11
Form: DRS/A
Chunk 260
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 no amendment or termination shall be made that would materially and adversely affect the rights of any participant under any outstanding stock award without the participant’s consent. The Company shall obtain stockholder approval of any amendment to the 2018 Plan to the extent necessary to comply with appliable laws. The 2018 Plan provides that it will terminate automatically ten years after adoption, provided, however, it will terminate earlier upon the completion of this offering, but as noted above, awards outstanding under the 2018 Plan will remain outstanding and will continue to be governed by their existing terms. Employee stock purchase plan General Our ESPP was adopted by our Board of Directors on , 2025, approved by our stockholders on , 2025 and will become effective upon the effectiveness of the registration statement of which this prospectus forms a part. The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the Code. Share reserve shares of our Class A common stock have been reserved for issuance under our ESPP. The number of shares reserved for issuance under our ESPP will automatically be increased on the first business day of each of our fiscal years, commencing in 2026 and ending in 2036, by a number equal to the least of:

| • |     | shares; |

| • |     | % of the shares of Class A common stock outstanding on the last business day of the prior fiscal year; or |

| • |     | the number of shares determined by our Board of Directors. |

The number of shares reserved under our ESPP will automatically be adjusted in the event of a stock split, stock dividend or a reverse stock split (including an adjustment to the per-purchaseperiod share limit). Administration The compensation committee of our Board of Directors will administer our ESPP. 201

Eligibility

All of our
employees will be eligible to participate if we employ them for more than 20 hours per week and for five or more months per year. Eligible employees may begin participating in our ESPP at the start of any offering period.

Offering periods

Each offering period will last a number of months
determined by the compensation committee, not to exceed 27 months. A new offering period will begin periodically, as determined by the compensation committee. Offering periods may overlap or may be consecutive. Unless otherwise determined by the
compensation committee, two offering periods of six months’ duration will begin in each year on and . Unless otherwise determined by the administrator, the first offering