Quantum-Si CPO sells shares for tax withholding

Quantum-Si Chief Product Officer John S. Vieceli reported mandatory sales of 21,997 shares of Class A common stock to cover tax withholding on vested RSUs.

Rhea-AI Filing Summary

Quantum-Si Chief Product Officer John S. Vieceli reported mandatory sales of 21,997 shares of Class A common stock to cover tax withholding on vested RSUs. The shares were sold in open-market transactions on March 20 and March 23 at weighted average prices around $0.83–$0.85 per share.

The filing explains these sales occurred under a pre-set, mandatory sell-to-cover provision established when the restricted stock units were granted, which he cannot alter. After these transactions, he directly holds 1,170,657 shares, so the sale represents a small portion of his overall stake.

Insider Trade Summary

Net Seller: 21,997 shares

Net Sell 2 txns

Insider Vieceli John S.

Role Chief Product Officer

Sold 21,997 shs ($18K)

Type	Security	Shares	Price	Value
Sale	Class A Common Stock	11,239	$0.8266	$9K
Sale	Class A Common Stock	10,758	$0.8483	$9K

Holdings After Transaction: Class A Common Stock — 1,170,657 shares (Direct)

Footnotes (3)

1. F1. Represents shares sold pursuant to a mandatory Quantum-Si sell-to-cover provision for required federal, state and local withholding taxes in connection with the vesting of previously granted restricted stock units. Individual is not able to alter this mandatory sell-to-cover provision that is enacted at the grant date of the related restricted stock unit award.
2. F2. Represents the weighted average sales price per share. The shares sold at prices ranging from $0.8314 to $0.8718 per share. Full information regarding the number of shares sold at each price shall be provided upon request to the staff of the U.S. Securities and Exchange Commission, the Issuer, or a security holder of the Issuer.
3. F3. Represents the weighted average sales price per share. The shares sold at prices ranging from $0.7973 to $0.8525 per share. Full information regarding the number of shares sold at each price shall be provided upon request to the staff of the U.S. Securities and Exchange Commission, the Issuer, or a security holder of the Issuer.

FAQ

What did Quantum-Si (QSI) Chief Product Officer John S. Vieceli report in this Form 4?

He reported selling 21,997 shares of Quantum-Si Class A common stock. These sales were tied to tax withholding on vested restricted stock units, executed under a mandatory, pre-set sell-to-cover provision he cannot change.

Were John S. Vieceli’s Quantum-Si (QSI) share sales discretionary trades?

No, the sales were not discretionary. The filing states they were executed under a mandatory Quantum-Si sell-to-cover provision for required federal, state, and local taxes when previously granted restricted stock units vested.

How many Quantum-Si (QSI) shares did John S. Vieceli sell and at what prices?

He sold a total of 21,997 shares. One block of 10,758 shares sold at a weighted average of about $0.8483 and another 11,239 shares at about $0.8266, with actual trade prices spanning narrow ranges around those levels.

How many Quantum-Si (QSI) shares does John S. Vieceli hold after these Form 4 transactions?

After the reported sales, he directly holds 1,170,657 shares of Quantum-Si Class A common stock. This indicates the tax-related transactions affected only a relatively small portion of his overall reported equity position.

Why were Quantum-Si (QSI) shares sold in connection with restricted stock unit vesting?

Shares were sold to satisfy required federal, state, and local tax withholding obligations when previously granted restricted stock units vested. The company’s mandatory sell-to-cover provision automatically triggered these sales rather than leaving the tax payment decision to the individual.

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Accepted by SEC EDGAR 03/24/2026 - 06:55 PM Learn about SEC filing dates

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Vieceli John S.

(Last) (First) (Middle)

C/O QUANTUM-SI INCORPORATED

29 BUSINESS PARK DRIVE

(Street)

BRANFORD CONNECTICUT 06405

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Quantum-Si Inc [ QSI ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chief Product Officer

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
03/20/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Class A Common Stock	03/20/2026		S(1)		10,758	D	$0.8483(2)	1,181,896	D
Class A Common Stock	03/23/2026		S(1)		11,239	D	$0.8266(3)	1,170,657	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. Represents shares sold pursuant to a mandatory Quantum-Si sell-to-cover provision for required federal, state and local withholding taxes in connection with the vesting of previously granted restricted stock units. Individual is not able to alter this mandatory sell-to-cover provision that is enacted at the grant date of the related restricted stock unit award.

2. Represents the weighted average sales price per share. The shares sold at prices ranging from $0.8314 to $0.8718 per share. Full information regarding the number of shares sold at each price shall be provided upon request to the staff of the U.S. Securities and Exchange Commission, the Issuer, or a security holder of the Issuer.

3. Represents the weighted average sales price per share. The shares sold at prices ranging from $0.7973 to $0.8525 per share. Full information regarding the number of shares sold at each price shall be provided upon request to the staff of the U.S. Securities and Exchange Commission, the Issuer, or a security holder of the Issuer.

	/s/ Christian LaPointe, Ph.D., Attorney-in-Fact.	03/24/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)