X0508 4 2025-11-06 0002070849 BillionToOne, Inc. BLLN 0002087908 Ileri Firat SQUARE VICTORIA REGAIN 1 SINT-JOOST-TEN-NODE C9 1210 BELGIUM true false true false false Common Stock 2025-11-06 4 A false 8333 0 A 8333 D Common Stock 2025-11-07 4 C false 28981 A 37314 D Common Stock 2025-11-07 4 C false 640727 A 640727 I See Footnotes Common Stock 2025-11-07 4 C false 18845 A 18845 I See Footnotes Common Stock 2025-11-07 4 C false 2015118 A 2015118 I See Footnotes Common Stock 2025-11-07 4 C false 2451665 A 2631664 I See Footnotes Common Stock 2025-11-07 4 C false 2580833 A 2580833 I See Footnotes Common Stock 2025-11-07 4 J false 37314 D 0 D Common Stock 2025-11-07 4 J false 640727 D 0 I See Footnotes Common Stock 2025-11-07 4 J false 18845 D 0 I See Footnotes Common Stock 2025-11-07 4 J false 2015118 D 0 I See Footnotes Common Stock 2025-11-07 4 J false 2631664 D 0 I See Footnotes Common Stock 2025-11-07 4 J false 2580833 D 0 I See Footnotes Class A Common Stock 2025-11-07 4 J false 37314 A 37314 D Class A Common Stock 2025-11-07 4 J false 640727 A 640727 I See Footnotes Class A Common Stock 2025-11-07 4 J false 18845 A 18845 I See Footnotes Class A Common Stock 2025-11-07 4 J false 2015118 A 2015118 I See Footnotes Class A Common Stock 2025-11-07 4 J false 2631664 A 2631664 I See Footnotes Class A Common Stock 2025-11-07 4 J false 2580833 A 2580833 I See Footnotes Series A-6 Convertible Preferred Stock 2025-11-07 4 C false 28981 D Common Stock 28981 0 D Series B-2 Convertible Preferred Stock 2025-11-07 4 C false 640727 D Common Stock 640727 0 I See Footnotes Series B-1 Convertible Preferred Stock 2025-11-07 4 C false 18845 D Common Stock 18845 0 I See Footnotes Series C Convertible Preferred Stock 2025-11-07 4 C false 1569015 D Common Stock 1569015 0 I See Footnotes Series D Convertible Preferred Stock 2025-11-07 4 C false 446103 D Common Stock 446103 0 I See Footnotes Series A-1 Convertible Preferred Stock 2025-11-07 4 C false 20000 D Common Stock 20000 0 I See Footnotes Series A-2 Convertible Preferred Stock 2025-11-07 4 C false 33000 D Common Stock 33000 0 I See Footnotes Series B-1 Convertible Preferred Stock 2025-11-07 4 C false 2261377 D Common Stock 2261377 0 I See Footnotes Series C Convertible Preferred Stock 2025-11-07 4 C false 137288 D Common Stock 137288 0 I See Footnotes Series A-6 Convertible Preferred Stock 2025-11-07 4 C false 2260520 D Common Stock 2260520 0 I See Footnotes Series B-2 Convertible Preferred Stock 2025-11-07 4 C false 320363 D Common Stock 320363 0 I See Footnotes Each restricted stock unit ("RSU") represents a contingent right to receive one share of the Issuer's Common Stock. The RSUs shall vest over three years in equal annual installments on the anniversary of November 6, 2025, subject to the Reporting Person's continuous service to the Issuer through each such vesting date. The total represents shares received upon conversion of shares of Series A-1 Convertible Preferred Stock, Series A-2 Convertible Preferred Stock, Series A-6 Convertible Preferred Stock, Series B-1 Convertible Preferred Stock, Series B-2 Convertible Preferred Stock, Series C Convertible Preferred Stock and/or Series D Convertible Preferred Stock. The reported security converted into the Issuer's Common Stock on a one-for-one basis automatically immediately prior to the closing of the Issuer's initial public offering of Class A common stock (the "Offering") without payment of further consideration. The shares have no expiration date. The reported security is directly held by HB&Q NV (HB&Q COMPARTMENT III). The reported security is directly held by Hummingbird Collective CommV. The reported security is directly held by Hummingbird Dragons CommV. The reported security is directly held by Hummingbird Opportunity Fund II CommV. The reported security is directly held by Hummingbird Ventures III CommV. Humming Bird Ventures Management NV is the managing member of Hummingbird Opportunity Fund II CommV, Hummingbird Ventures III CommV, Hummingbird Dragons CommV, Hummingbird Collective CommV, and HB&Q NV (HB&Q COMPARTMENT III) (the Hummingbird Funds) and, as a result, may be deemed to beneficially own shares held by the Hummingbird Funds. Mr. Ileri, Barend Van den Brande, and Lukas Decoster are partners of Hummingbird Ventures Management NV and may be deemed to have shared voting and investment power over the shares held by the Hummingbird Funds. The Reporting Person disclaims beneficial ownership of these shares except to the extent of his pecuniary interest therein. 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 Offering. /s/ Thomas P. Lynch, Attorney-in-Fact 2025-11-10