X0508 4 2025-11-07 0 0002070849 BillionToOne, Inc. BLLN 0002099044 Humming Bird Ventures Management NV SQUARE VICTORIA REGAIN 1 SINT-JOOST-TEN-NODE C9 1210 BELGIUM 0 0 1 0 0002099049 Hummingbird Opportunity Fund II CommV SQUARE VICTORIA REGAIN 1 SINT-JOOST-TEN-NODE C9 1210 BELGIUM 0 0 1 0 0002099047 Hummingbird Ventures III CommV SQUARE VICTORIA REGAIN 1 SINT-JOOST-TEN-NODE C9 1210 BELGIUM 0 0 1 0 0002099040 Hummingbird Dragons CommV SQUARE VICTORIA REGAIN 1 SINT-JOOST-TEN-NODE C9 1210 BELGIUM 0 0 1 0 0002099041 Hummingbird Collective CommV SQUARE VICTORIA REGAIN 1 SINT-JOOST-TEN-NODE C9 1210 BELGIUM 0 0 1 0 0002099035 HB&Q NV (HB&Q COMPARTMENT III) SQUARE VICTORIA REGAIN 1 SINT-JOOST-TEN-NODE C9 1210 BELGIUM 0 0 1 0 0002099027 Van den Brande Barend SQUARE VICTORIA REGAIN 1 SINT-JOOST-TEN-NODE C9 1210 BELGIUM 0 0 1 0 0002099021 Decoster Lukas SQUARE VICTORIA REGAIN 1 SINT-JOOST-TEN-NODE C9 1210 BELGIUM 0 0 1 0 0 Common Stock 2025-11-07 4 C 0 640727 A 640727 I See Footnotes Common Stock 2025-11-07 4 C 0 18845 A 18845 I See Footnotes Common Stock 2025-11-07 4 C 0 2015118 A 2015118 I See Footnotes Common Stock 2025-11-07 4 C 0 2451665 A 2631664 I See Footnotes Common Stock 2025-11-07 4 C 0 2580833 A 2580833 I See Footnotes Common Stock 2025-11-07 4 J 0 640727 D 0 I See Footnotes Common Stock 2025-11-07 4 J 0 18845 D 0 I See Footnotes Common Stock 2025-11-07 4 J 0 2015118 D 0 I See Footnotes Common Stock 2025-11-07 4 J 0 2631664 D 0 I See Footnotes Common Stock 2025-11-07 4 J 0 2580833 D 0 I See Footnotes Class A Common Stock 2025-11-07 4 J 0 640727 A 640727 I See Footnotes Class A Common Stock 2025-11-07 4 J 0 18845 A 18845 I See Footnotes Class A Common Stock 2025-11-07 4 J 0 2015118 A 2015118 I See Footnotes Class A Common Stock 2025-11-07 4 J 0 2631664 A 2631664 I See Footnotes Class A Common Stock 2025-11-07 4 J 0 2580833 A 2580833 I See Footnotes Series B-2 Convertible Preferred Stock 2025-11-07 4 C 0 640727 D Common Stock 640727 0 I See Footnotes Series B-1 Convertible Preferred Stock 2025-11-07 4 C 0 18845 D Common Stock 18845 0 I See Footnotes Series C Convertible Preferred Stock 2025-11-07 4 C 0 1569015 D Common Stock 1569015 0 I See Footnotes Series D Convertible Preferred Stock 2025-11-07 4 C 0 446103 D Common Stock 446103 0 I See Footnotes Series A-1 Convertible Preferred Stock 2025-11-07 4 C 0 20000 D Common Stock 20000 0 I See Footnotes Series A-2 Convertible Preferred Stock 2025-11-07 4 C 0 33000 D Common Stock 33000 0 I See Footnotes Series B-1 Convertible Preferred Stock 2025-11-07 4 C 0 2261377 D Common Stock 2261377 0 I See Footnotes Series C Convertible Preferred Stock 2025-11-07 4 C 0 137288 D Common Stock 137288 0 I See Footnotes Series A-6 Convertible Preferred Stock 2025-11-07 4 C 0 2260520 D Common Stock 2260520 0 I See Footnotes Series B-2 Convertible Preferred Stock 2025-11-07 4 C 0 320363 D Common Stock 320363 0 I See Footnotes 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 Persons disclaim beneficial ownership of these shares except to the extent of their pecuniary interests 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. Hummingbird Ventures Management NV /s/ Lukas Decoster 49/9 CommV, represented by its permanent representative Lukas Decoster, Director 2026-01-20 /s/ Barend Van den Brande 2026-01-20 /s/ Lukas Decoster 2026-01-20 Hummingbird Opportunity Fund II CommV /s/ Firat Ileri By: Hummingbird Ventures Management NV, its Manager By: Firat Ileri, Permanent Representative 2026-01-20 Hummingbird Ventures III CommV /s/ Firat Ileri By: Hummingbird Ventures Management NV, its Manager By: Firat Ileri, Permanent Representative 2026-01-20 Hummingbird Dragons CommV /s/ Firat Ileri By: Hummingbird Ventures Management NV, its Manager By: Firat Ileri, Permanent Representative 2026-01-20 Hummingbird Collective CommV /s/ Firat Ileri By: Hummingbird Ventures Management NV, its Manager By: Firat Ileri, Permanent Representative 2026-01-20 HB&Q NV /s/ Firat Ileri By: Hummingbird Ventures Management NV, its Manager By: Firat Ileri, Permanent Representative 2026-01-20