Form 4 Filing for Anthony Pagano

On June 10, 2026, Anthony Pagano was granted 3,017 restricted stock units (RSUs) of BillionToOne, Inc. Class A Common Stock. These RSUs are subject to a service-based vesting requirement, which will be satisfied on the earlier of the next annual stockholder meeting or the one-year anniversary of June 10, 2026. Following this grant, Mr. Pagano directly owns 7,913 shares of Class A Common Stock. The filing was signed by Thomas Lynch, Attorney-in-Fact, on June 11, 2026.