X0508 4 2025-11-07 0002070849 BillionToOne, Inc. BLLN 0002087126 ten Bosch John Roderick C/O BILLIONTOONE, INC. 1035 O'BRIEN DRIVE MENLO PARK CA 94025 false true false false See Remarks false Common Stock 2025-11-07 4 J false 37000 D 0 D Class A Common Stock 2025-11-07 4 J false 37000 A 37000 D Class A Common Stock 2025-11-07 4 P false 800 60 A 37800 D Stock Option (right to buy) 0.56 2025-11-07 4 J false 28500 D 2030-09-30 Common Stock 28500 0 D Stock Option (right to buy) 0.56 2025-11-07 4 J false 28500 A 2030-09-30 Class A Common Stock 28500 28500 D Stock Option (right to buy) 2.8 2025-11-07 4 J false 20000 D 2031-06-07 Common Stock 20000 0 D Stock Option (right to buy) 2.8 2025-11-07 4 J false 20000 A 2031-06-07 Class A Common Stock 20000 20000 D Stock Option (right to buy) 10.92 2025-11-07 4 J false 15000 D 2032-08-01 Common Stock 15000 0 D Stock Option (right to buy) 10.92 2025-11-07 4 J false 15000 A 2032-08-01 Class A Common Stock 15000 15000 D Stock Option (right to buy) 15.17 2025-11-07 4 J false 30000 D 2034-06-05 Common Stock 30000 0 D Stock Option (right to buy) 15.17 2025-11-07 4 J false 30000 A 2034-06-05 Class A Common Stock 30000 30000 D Stock Option (right to buy) 30.78 2025-11-07 4 J false 37500 D 2035-09-30 Common Stock 37500 0 D Stock Option (right to buy) 30.78 2025-11-07 4 J false 37500 A 2035-09-30 Class A Common Stock 37500 37500 D Pursuant to a reclassification exempt under Rule 16b-7, each share of Common Stock was automatically reclassified into one share of Class A common stock immediately prior to the completion of the Issuer's initial public offering of Class A common stock (the "Offering"). These shares of Class A common stock were purchased by the Reporting Person through a directed share program in connection with the Offering. The options are fully vested and exercisable. The options are subject to a service-based vesting requirement, which shall be satisfied over a four-year period. The options vest and become exercisable in equal monthly installments commencing on April 1, 2022, subject to the Reporting Person's continuous service with the Issuer through each such vesting date. The options are subject to a service-based vesting requirement, which shall be satisfied over a four-year period. The options vest and become exercisable in equal monthly installments commencing on May 15, 2024, subject to the Reporting Person's continuous service with the Issuer through each such vesting date. The options are subject to a service-based vesting requirement, which shall be satisfied over a four-year period. The options vest and become exercisable in equal monthly installments commencing on September 15, 2025, subject to the Reporting Person's continuous service with the Issuer through each such vesting date. Senior Vice President of Laboratory Operations /s/ Thomas P. Lynch, Attorney-in-Fact 2025-11-12