[SCHEDULE 13D/A] Quantum-Si Incorporated SEC Filing

Rhea-AI Filing Summary

Jonathan M. Rothberg and affiliated entities disclosed holdings in Quantum-Si Inc. across both Class A and Class B stock classes and filed Amendment No. 4 to their Schedule 13D. For Class A, the filing reports beneficial ownership of 14,276,415 shares, representing 7.8% of the 182,557,698 Class A shares outstanding as of July 31, 2025; that amount includes personal shares, options exercisable within 60 days, and shares held by trusts and affiliated entities.

The filing also reports beneficial ownership of 19,937,500 Class B shares, representing 100% of outstanding Class B stock. As part of estate planning, trusts for Dr. Rothberg's children adopted a Rule 10b5-1 trading plan allowing sales of up to 8,973,841 Class A shares during the plan period from January 14, 2026 through January 14, 2027, subject to minimum price parameters; no assurance any sales will occur. The amendment adds the Rule 10b5-1 plan as Exhibit 5.

Positive

• Full disclosure of holdings across Class A and Class B common stock, including options and affiliated entities, increases transparency
• Adoption of a Rule 10b5-1 trading plan provides a pre-established, compliant mechanism for potential sales and reduces risk of ad hoc insider selling
• Attachment of Exhibit 5 documents the trading plan and supplements the Schedule 13D record

Negative

• Trading plan authorizes sale of up to 8,973,841 Class A shares during January 14, 2026 to January 14, 2027, which could increase free float if executed
• Concentrated control remains with Dr. Rothberg and affiliated entities via 100% ownership of Class B shares, maintaining governance concentration

Insights

Corporate Governance Expert

TL;DR: Large founder holdings and a planned Rule 10b5-1 sale increase transparency but preserve existing control through Class B shares.

The filing confirms concentrated governance: Dr. Rothberg and affiliated entities control 100% of Class B stock, which typically carries disproportionate voting power, and retain a meaningful economic stake in Class A shares. The addition of a Rule 10b5-1 plan documents a prearranged, compliant mechanism for potential disposition of nearly nine million Class A shares held by trusts. That increases disclosure and reduces ad hoc insider selling risk while signaling estate planning activity. From a governance perspective, no change-in-control actions or contested governance matters are disclosed.

Estate Planning / Securities Counsel

TL;DR: The scheduled Rule 10b5-1 plan is a routine, compliance-oriented step in estate planning; it formalizes potential future sales.

The amendment explicitly ties the potential sale of up to 8,973,841 Class A shares to a Rule 10b5-1 plan with a defined plan sales period and minimum price parameters. This structure is consistent with standard estate liquidity planning while reducing timing risk of opportunistic insider sales. The filing includes Exhibit 5 to document the plan, improving regulatory disclosure. No legal proceedings or other estate-related transactions are described in this amendment.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 4)

Quantum-Si Inc

(Name of Issuer)

Class A common stock, par value $0.0001 per share, Class B common stock, par value $0.0001 per share

(Title of Class of Securities)

74765K105

(CUSIP Number)

Jonathan M. Rothberg, Ph.D.
c/o Quantum-Si Incorporated, 29 Business Park Drive
Branford, CT, 06405
(866) 688-7374

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

09/09/2025

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

SCHEDULE 13D

CUSIP No. 74765K105

1

Name of reporting person

ROTHBERG JONATHAN M

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

PF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 12,085,926.00
8	Shared Voting Power 2,190,489.00
9	Sole Dispositive Power 12,085,926.00
10	Shared Dispositive Power 2,190,489.00

11

Aggregate amount beneficially owned by each reporting person

14,276,415.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

7.8 %

14

Type of Reporting Person (See Instructions)

IN

Comment for Type of Reporting Person:

This Reporting Person's Table is for Class A common stock. Rows 7, 9 and 11 consists of (i) 2,568,443 shares of Class A common stock of Quantum-Si Incorporated (the ''Issuer'') held by Jonathan M. Rothberg, Ph.D., (ii) stock options to purchase 543,642 shares of Class A common stock of the Issuer which are exercisable within 60 days of September 9, 2025, held by Dr. Jonathan M. Rothberg and (iii) an aggregate of 8,973,841 shares of Class A common stock of the Issuer held by entities owned by trusts created for the benefit of Dr. Jonathan Rothberg's children, including shares of Class A common stock previously distributed from 2012 JMR Trust Common, LLC. Rows 8, 10 and 11 consists of (i) 1,917,067 shares of Class A common stock of the Issuer held by 23rd Century Capital LLC, and (ii) 273,422 shares of Class A common stock of the Issuer held by Dr. Jonathan Rothberg's spouse, Bonnie E. Gould Rothberg, M.D. Row 13 is calculated based on 182,557,698 shares of Class A common stock of the Issuer outstanding as of July 31, 2025.

SCHEDULE 13D

CUSIP No. 74765K105

1

Name of reporting person

ROTHBERG JONATHAN M.

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

PF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 19,937,500.00
8	Shared Voting Power 0.00
9	Sole Dispositive Power 19,937,500.00
10	Shared Dispositive Power 0.00

11

Aggregate amount beneficially owned by each reporting person

19,937,500.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

100 %

14

Type of Reporting Person (See Instructions)

IN

Comment for Type of Reporting Person:

This Reporting Person's Table is for Class B common stock. Rows 7, 9 and 11 consists of (i) 17,943,750 shares of Class B common stock of the Issuer held by 4C Holdings I, LLC and (ii) 1,993,750 shares of Class B common stock of the Issuer held by 4C Holdings V, LLC. Row 13 is calculated based on 19,937,500 shares of Class B common stock of the Issuer outstanding as of July 31, 2025.

SCHEDULE 13D

CUSIP No. 74765K105

1

Name of reporting person

23rd Century Capital LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

PF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power
8	Shared Voting Power 1,917,067.00
9	Sole Dispositive Power
10	Shared Dispositive Power 1,917,067.00

11

Aggregate amount beneficially owned by each reporting person

1,917,067.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

1.05 %

14

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person:

This Reporting Person's table is for Class A common stock. Row 13 is calculated based on 182,557,698 shares of Class A common stock of the Issuer outstanding as of July 31, 2025.

SCHEDULE 13D

CUSIP No. 74765K105

1

Name of reporting person

2012 JMR Trust Common, LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

PF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power
8	Shared Voting Power
9	Sole Dispositive Power
10	Shared Dispositive Power

11

Aggregate amount beneficially owned by each reporting person

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

0 %

14

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person:

This Reporting Person's table is for Class A common stock. Row 13 is calculated based on 182,557,698 shares of Class A common stock of the Issuer outstanding as of July 31, 2025.

SCHEDULE 13D

CUSIP No. 74765K105

1

Name of reporting person

4C Holdings I, LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

PF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power
8	Shared Voting Power 17,943,750.00
9	Sole Dispositive Power
10	Shared Dispositive Power 17,943,750.00

11

Aggregate amount beneficially owned by each reporting person

17,943,750.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

90 %

14

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person:

This Reporting Person's table is for Class B common stock. Row 13 is calculated based on 19,937,500 shares of Class B common stock of the Issuer outstanding as of July 31, 2025.

SCHEDULE 13D

CUSIP No. 74765K105

1

Name of reporting person

4C Holdings V, LLC

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

PF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power
8	Shared Voting Power 1,993,750.00
9	Sole Dispositive Power
10	Shared Dispositive Power 1,993,750.00

11

Aggregate amount beneficially owned by each reporting person

1,993,750.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

10 %

14

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person:

This Reporting Person's table is for Class B common stock. Row 13 is calculated based on 19,937,500 shares of Class B common stock of the Issuer outstanding as of July 31, 2025.

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Class A common stock, par value $0.0001 per share, Class B common stock, par value $0.0001 per share
(b)	Name of Issuer: Quantum-Si Inc
(c)	Address of Issuer's Principal Executive Offices: 29 BUSINESS PARK DRIVE, BRANFORD, CONNECTICUT , 06405.
Item 1 Comment: Explanatory Note Amendment No. 4 to Schedule 13D ("Amendment No. 4") amends and supplements the Schedule 13D dated June 18, 2021, as amended by Amendment No. 1 filed on September 13, 2023, Amendment No. 2 filed on September 17, 2024 and Amendment No. 3 filed on December 31, 2024 (collectively, as amended, the "Schedule 13D") relating to the Class A common stock, par value $0.0001 per share ("Class A common stock"), and Class B common stock, par value $0.0001 per share, of Quantum-Si Incorporated, a Delaware corporation. Information reported in the Schedule 13D remains in effect except to the extent that it is amended, restated or superseded by information contained in this Amendment No. 4. Capitalized terms used but not defined herein have the meanings ascribed to them in the Schedule 13D.
Item 4.	Purpose of Transaction
	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 5. Pursuant to the Plan, sales of up to 8,973,841 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 14, 2026 and ending on January 14, 2027 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 7.	Material to be Filed as Exhibits.
	Item 7 of the Schedule 13D is hereby amended by adding the following exhibit: 5. Rule 10b5-1 Trading Plan

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

ROTHBERG JONATHAN M

Signature:	/s/ Jonathan M. Rothberg
Name/Title:	Jonathan M. Rothberg, Ph.D.
Date:	09/11/2025

ROTHBERG JONATHAN M.

Signature:	/s/ Jonathan M. Rothberg
Name/Title:	Jonathan M. Rothberg, Ph.D.
Date:	09/11/2025

23rd Century Capital LLC

Signature:	/s/ Jonathan M. Rothberg
Name/Title:	Jonathan M. Rothberg, Ph.D., Member
Date:	09/11/2025

2012 JMR Trust Common, LLC

Signature:	/s/ Jonathan M. Rothberg
Name/Title:	Jonathan M. Rothberg, Ph.D., Manager
Date:	09/11/2025

4C Holdings I, LLC

Signature:	/s/ Jonathan M. Rothberg
Name/Title:	Jonathan M. Rothberg, Ph.D., Manager
Date:	09/11/2025

4C Holdings V, LLC

Signature:	/s/ Jonathan M. Rothberg
Name/Title:	Jonathan M. Rothberg, Ph.D., Manager
Date:	09/11/2025

FAQ

What does Jonathan M. Rothberg report owning in Quantum-Si (QSI)?

The filing reports beneficial ownership of 14,276,415 Class A shares (7.8% of Class A) and 19,937,500 Class B shares (100% of Class B) as of the filing.

What is the Rule 10b5-1 trading plan disclosed in the amendment?

Entities owned by trusts for Dr. Rothberg's children adopted a Rule 10b5-1 plan authorizing sales of up to 8,973,841 Class A shares from January 14, 2026 through January 14, 2027, subject to minimum price parameters.

Will sales under the trading plan definitely occur?

No. The filing explicitly states there is no assurance that any shares will be sold under the Plan.

What Exhibit was added to the Schedule 13D by this amendment?

Item 7 was amended to add Exhibit 5, the Rule 10b5-1 Trading Plan.

How many Class A shares outstanding were used to calculate percentages?

Percentages are calculated based on 182,557,698 Class A shares outstanding as of July 31, 2025, per the filing.

Does the filing disclose any change of control or litigation?

No. The amendment does not disclose any change of control actions or legal proceedings; it focuses on holdings and the trading plan.