As of November 7, 2026, one holder's latest Schedule 13D or 13G filing report owning 5% or more of Quantum-Si Inc. The largest reported stake is Rothberg Jonathan M's, at 100%. 5 filings are on record since July 29, 2025 (Schedule 13D/A, August 28, 2026).
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Key facts
- · Reporting person: Rothberg Jonathan M · Sole voting: 12,185,926 · Shared voting: 2,190,489 · Sole dispositive: 12,185,926 · Shared dispositive: 2,190,489 · SCHEDULE 13D/A, 2026-08-28
- · Reporting person: BlackRock, Inc. · Sole voting: 4,598,208 · Shared voting: 0 · Sole dispositive: 4,598,208 · Shared dispositive: 0 · SCHEDULE 13G/A, 2026-07-29
- · Holder: The Vanguard Group · Percent: 4.77% · SCHEDULE 13G/A
- · Holder: Rothberg Jonathan M · Percent: 100% · SCHEDULE 13D/A
- · Holder: The Vanguard Group · Percent: 5.3% · SCHEDULE 13G
Quantum-Si Inc has 5 Schedule 13D or 13G filings on record since 2025-07-29. 1 holder's latest filing reports 5% or more of class a common stock, par value $0.0001 per share, class b common stock, par value $0.0001 per share. Each figure below is the holder's own, as filed, with the filing linked.
Holders
| Holder | Percent | Shares | Latest | Event date |
|---|---|---|---|---|
| 100% | 14,376,415 | SCHEDULE 13D/A, 2026-08-28 | 2026-08-26 | |
| The Vanguard Group | 4.77% | 8,714,507 | SCHEDULE 13G/A, 2025-10-30 | 2025-09-30 |
| BlackRock, Inc. | 2.3% | 4,598,208 | SCHEDULE 13G/A, 2026-07-29 | 2026-06-30 |
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More on Quantum-Si Inc and the records around it.
Quantum-Si Inc elsewhere on the record
Companies that share a holder
- ROTHBERG JONATHAN M also filed stake reports on 1 other company: Butterfly Network, Inc. (Aug 2026)
- BlackRock, Inc. also filed stake reports on 1596 other companies: AvePoint, Inc. (Nov 2026), BIOMARIN PHARMACEUTICAL INC (Nov 2026), MSG RANGERS CORP (Nov 2026)
- The Vanguard Group also filed stake reports on 2384 other companies: BellRing Brands, Inc. (Sep 2026), CAL-MAINE FOODS INC (Sep 2026), FTAI Aviation Ltd. (Sep 2026)
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Voting and dispositive power, as filed
| Reporting person | Sole voting | Shared voting | Sole dispositive | Shared dispositive | Filing |
|---|---|---|---|---|---|
| Rothberg Jonathan M | 12,185,926 | 2,190,489 | 12,185,926 | 2,190,489 | SCHEDULE 13D/A, 2026-08-28 |
| Rothberg Jonathan M. | 19,937,500 | 0 | 19,937,500 | 0 | SCHEDULE 13D/A, 2026-08-28 |
| 23rd Century Capital LLC | 0 | 1,917,067 | 0 | 1,917,067 | SCHEDULE 13D/A, 2026-08-28 |
| 4C Holdings I, LLC | 0 | 17,943,750 | 0 | 17,943,750 | SCHEDULE 13D/A, 2026-08-28 |
| 4C Holdings V, LLC | 0 | 1,993,750 | 0 | 1,993,750 | SCHEDULE 13D/A, 2026-08-28 |
| BlackRock, Inc. | 4,598,208 | 0 | 4,598,208 | 0 | SCHEDULE 13G/A, 2026-07-29 |
The latest filing identifies Quantum-Si Inc by CUSIP 74765K105 and gives its principal executive office as 29 BUSINESS PARK DRIVE, BRANFORD, CT 06405 (SCHEDULE 13D/A, 2026-08-28).
Purpose of Transaction (Item 4)
Rothberg Jonathan M
In connection with estate planning, entities owned by trusts created for the benefit of Dr. Jonathan Rothberg's children have entered into a trading plan pursuant to Rule 10b5-1 under the Securities Exchange Act of 1934, as amended (the "Plan"), a copy of which is attached hereto as Exhibit 6. Pursuant to the Plan, sales of up to 8,947,746 shares of Class A common stock may be effected during the plan sales period beginning following the cooling-off period contained in Rule 10b5-1(c) on January 15, 2027 and ending on January 15, 2028 in accordance with the terms and conditions of the Plan. The sale of shares of Class A common stock under the Plan is subject to minimum price parameters included in the Plan, and there is no assurance that any shares of Class A common stock will be sold under the Plan.Item 4 of the SCHEDULE 13D/A filed 2026-08-28
Timeline
| Filed | Holder | Percent | Filing |
|---|---|---|---|
| 2025-07-29 | The Vanguard Group | 5.3% | SCHEDULE 13G |
| 2025-09-11 | Rothberg Jonathan M | 100% | SCHEDULE 13D/A |
| 2025-10-30 | The Vanguard Group | 4.77% | SCHEDULE 13G/A |
| 2026-07-29 | BlackRock, Inc. | 2.3% | SCHEDULE 13G/A |
| 2026-08-28 | Rothberg Jonathan M | 100% | SCHEDULE 13D/A |
Questions about who owns Quantum-Si Inc
Who owns Quantum-Si Inc?
On this page, one holder's latest ownership filing reports 5% or more of Quantum-Si Inc: Rothberg Jonathan M (100%, Schedule 13D/A, filed 2026-08-28).
When did Rothberg Jonathan M buy into Quantum-Si Inc?
The filings give report dates, not purchase dates. The earliest filing from Rothberg Jonathan M on this page is the Schedule 13D/A, filed 2025-09-11, reporting 100%; its latest, Schedule 13D/A filed 2026-08-28, reports 100%. That earliest filing is itself an amendment, which updates an earlier report.
Is this an audit or a full list?
Neither. The ownership list on this page covers only Schedule 13D and 13G filings, which holders make once they own 5% or more of a class of shares (an amendment can report a stake that has since fallen below 5%); 5 such filings are shown here. It is not an audit and not a full cap table: holders who never reached 5% are not listed, and a stake can change after its latest filing.
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Where this comes from
Anyone who comes to own more than 5% of a class of a listed company's voting shares has to tell the SEC. A holder who may seek to change or influence the company files Schedule 13D, and has to say in Item 4, "Purpose of Transaction", what it intends to do. A holder with no such intent, such as many index and passive funds, may file the shorter Schedule 13G. Both are amended when the stake changes, including when it falls below 5%.
Every row here is one of those filings, linked to the filing itself. Percentages and share counts are exactly as the holder filed them, for the holder the filing names; an amendment showing a lower figure is shown as filed. Item 4 text is quoted word for word. Where a 13D's Item 4 contains a sentence stating a definite intent to influence the company, that sentence is marked and quoted; the page does not describe the holder or its motives beyond the words it filed. Nothing here is investment advice.