SCHEDULE 13D/A

Prime Medicine Inc

Common Stock, $0.00001 par value · CUSIP: 74168J101

Event date: 2025-08-07

Reporting persons may disclose overlapping interests. Their amounts are shown individually and are not added into a filing total.

Filing-level shares

Unavailable

Percent of class

Unavailable

• ARCH Venture Fund X, L.P.Reported CIK 0001757011

  Shares: 18,486,894.00 · Class: 10.4%

• ARCH Venture Fund X Overage, L.P.Reported CIK 0001757017

  Shares: 18,486,894.00 · Class: 10.4%

• ARCH Venture Fund XII, L.P.Reported CIK 0001906837

  Shares: 18,486,894.00 · Class: 10.4%

• ARCH Venture Partners X, L.P.Reported CIK 0001782583

  Shares: 18,486,894.00 · Class: 10.4%

• ARCH Venture Partners X Overage, L.P.Reported CIK 0001768905

  Shares: 18,486,894.00 · Class: 10.4%

• ARCH Venture Partners XII, L.P.Reported CIK 0001979765

  Shares: 18,486,894.00 · Class: 10.4%

• ARCH Venture Partners X, LLCReported CIK 0001769012

  Shares: 18,486,894.00 · Class: 10.4%

• ARCH Venture Partners XII, LLCReported CIK 0001979548

  Shares: 18,486,894.00 · Class: 10.4%

• Robert NelsenReported CIK 0001219042

  Shares: 18,587,036.00 · Class: 10.4%

• Keith CrandellReported CIK 0001219039

  Shares: 18,486,894.00 · Class: 10.4%

• Kristina BurowReported CIK 0001569248

  Shares: 18,486,894.00 · Class: 10.4%

• Steven GillisReported CIK 0001229592

  Shares: 18,486,894.00 · Class: 10.4%

Amounts are as disclosed in this filing. Schedule type alone does not establish investment intent.