Quantum-Si Inc
QSI- Exchange
- Nasdaq
- Industry
- Measuring & Controlling Devices, NEC
- SEC CIK
- 0001816431
In the last 90 days, Quantum-Si Inc insiders filed 0 open-market purchases and 3 sales; 141 institutions reported holding it in 13F filings for Q2 2026, worth $46.8M in total; ARK Invest is the only superinvestor holding it.
Holders of 5% or more of QSI
Holders whose latest Schedule 13D or 13G filing reports 5% or more of Quantum-Si Inc, largest stake first. The change is against the holder's previous filing.
| Holder | Latest form | Stake | Change | First filed | Latest filing | Filing |
|---|---|---|---|---|---|---|
| Rothberg Jonathan M | 13D/A | 100.00%19.9M shares | 0.00 ppfrom 100.00% | Jun 21, 20216 filings | Aug 28, 2026 | SEC |
Stakes are as of each holder's latest filing. Holders whose last filing was in the old format (before December 18, 2024) have no stake on record and are not listed, and after an acquisition or delisting holders usually stop filing.
13D and 13G filings
40 Schedule 13D and 13G filings on Quantum-Si Inc, newest first, including old-format filings without a stake.
| Filed (ET) | Filer | Form | Stake | Change | Event date | Filing |
|---|---|---|---|---|---|---|
| Aug 28, 20265:35 PM ET | Rothberg Jonathan Mand 4 others | 13D/A | 100.00%19.9M shares | 0.00 ppfrom 100.00% | Aug 26, 2026 | SEC |
| Jul 29, 20263:19 PM ET | BlackRock, Inc. | 13G/A | 2.30%4.60M shares | –Below 5% | Jun 30, 2026 | SEC |
| Oct 30, 20253:50 PM ET | Vanguard Group Inc | 13G/A | 4.77%8.71M shares | −0.53 ppfrom 5.30%Below 5% | Sep 30, 2025 | SEC |
| Sep 11, 20255:04 PM ET | Rothberg Jonathan Mand 5 others | 13D/A | 100.00%19.9M shares | 0.00 ppfrom 100.00% | Sep 9, 2025 | SEC |
| Jul 29, 20252:22 PM ET | Vanguard Group Inc | 13G | 5.30%8.67M shares | New | Jun 30, 2025 | SEC |
| Jun 6, 20252:58 PM ET | ARK Investment Management LLCand 1 otherSuperinvestorARK Invest | 13G/A | 4.77%7.81M shares | −0.57 ppfrom 5.34%Below 5% | May 31, 2025 | SEC |
| May 14, 202510:42 AM ET | ARK Investment Management LLCand 1 otherSuperinvestorARK Invest | 13G/A | 5.34%8.71M shares | −1.87 ppfrom 7.21% | Mar 31, 2025 | SEC |
| Feb 14, 202511:23 AM ET | ARK Investment Management LLCSuperinvestorARK Invest | 13G/A | 7.21%8.85M shares | −2.46 ppfrom 9.67% | Dec 31, 2024 | SEC |
| Feb 13, 20253:35 PM ET | Nikko Asset Management Americas, Inc. | 13G/A | 4.85%5.97M shares | –Below 5% | Dec 31, 2024 | SEC |
| Feb 4, 20256:19 AM ET | Sumitomo Mitsui Trust Holdings, Inc.and 1 other | 13G/A | 4.80%5.97M shares | –Below 5% | Dec 31, 2024 | SEC |
| Jan 10, 20259:21 PM ET | ARK Investment Management LLCSuperinvestorARK Invest | 13G/A | 9.67%11.8M shares | – | Sep 30, 2024 | SEC |
| Dec 31, 20248:30 PM ET | Rothberg Jonathan Mand 5 others | 13D/A | 100.00%19.9M shares | – | Dec 27, 2024 | SEC |
| Sep 17, 2024 | Rothberg Jonathan M | 13D/AOld format | – | – | – | SEC |
| Jun 28, 2024 | Radcliffe Capital Management, L.P. | 13G/AOld format | – | – | – | SEC |
| Feb 13, 2024 | Nikko Asset Management Americas, Inc. | 13GOld format | – | New | – | SEC |
| Feb 5, 2024 | Sumitomo Mitsui Trust Holdings, Inc. | 13GOld format | – | New | – | SEC |
| Jan 29, 20245:25 PM ET | BlackRock Inc. | 13G/AOld format | – | – | – | SEC |
| Jan 29, 2024 | ARK Investment Management LLCSuperinvestorARK Invest | 13G/AOld format | – | – | – | SEC |
| Sep 13, 2023 | Rothberg Jonathan M | 13D/AOld format | – | – | – | SEC |
| Jul 10, 2023 | ARK Investment Management LLCSuperinvestorARK Invest | 13G/AOld format | – | – | – | SEC |
| Feb 14, 2023 | Glenview Capital Management, LLC | 13G/AOld format | – | – | – | SEC |
| Feb 10, 2023 | ARK Investment Management LLCSuperinvestorARK Invest | 13G/AOld format | – | – | – | SEC |
| Feb 3, 202312:10 PM ET | BlackRock Inc. | 13GOld format | – | New | – | SEC |
| Jun 28, 2022 | Foresite Capital Fund IV, L.P. | 13D/AOld format | – | – | – | SEC |
| Feb 14, 2022 | Radcliffe Capital Management, L.P. | 13G/AOld format | – | – | – | SEC |
| Feb 14, 2022 | Glazer Capital, LLC | 13G/AOld format | – | – | – | SEC |
| Feb 14, 2022 | Glenview Capital Management, LLC | 13G/AOld format | – | – | – | SEC |
| Feb 9, 2022 | ARK Investment Management LLCSuperinvestorARK Invest | 13G/AOld format | – | – | – | SEC |
| Feb 9, 2022 | Polar Asset Management Partners Inc. | 13G/AOld format | – | – | – | SEC |
| Jan 28, 2022 | Linden Capital L.P. | 13G/AOld format | – | – | – | SEC |
| Sep 10, 2021 | ARK Investment Management LLCSuperinvestorARK Invest | 13GOld format | – | New | – | SEC |
| Jun 21, 2021 | Foresite Capital Fund IV, L.P. | 13DOld format | – | New | – | SEC |
| Jun 21, 2021 | Rothberg Jonathan M | 13DOld format | – | New | – | SEC |
| Jun 14, 2021 | Flynn James E | 13D/AOld format | – | – | – | SEC |
| Mar 15, 2021 | Glenview Capital Management, LLC | 13GOld format | – | New | – | SEC |
| Feb 22, 2021 | Flynn James E | 13D/AOld format | – | – | – | SEC |
| Feb 16, 2021 | Radcliffe Capital Management, L.P. | 13G/AOld format | – | – | – | SEC |
| Feb 16, 2021 | Glazer Capital, LLC | 13GOld format | – | New | – | SEC |
| Feb 9, 2021 | Polar Asset Management Partners Inc. | 13GOld format | – | New | – | SEC |
| Jan 29, 2021 | Linden Capital L.P. | 13G/AOld format | – | – | – | SEC |
Form 144: proposed insider sales
Notices from officers, directors and other affiliates planning to sell Quantum-Si Inc shares.
No Form 144 notices for Quantum-Si Inc are on file.