SCHEDULE 13D/A

Quantum-Si Inc

Class A common stock, par value $0.0001 per share, Class B common stock, par value $0.0001 per share · CUSIP: 74765K105

Event date: 2025-09-09

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

• ROTHBERG JONATHAN MReported CIK 0001076352

  Shares: 14,276,415 · Class: 7.8%

• ROTHBERG JONATHAN M.

  Shares: 19,937,500 · Class: 100%

• 23rd Century Capital LLC

  Shares: 1,917,067 · Class: 1.05%

• 2012 JMR Trust Common, LLC

  Shares: Unavailable · Class: 0%

• 4C Holdings I, LLC

  Shares: 17,943,750 · Class: 90%

• 4C Holdings V, LLC

  Shares: 1,993,750 · Class: 10%

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