Tax-related share sale by Rapid Micro (RPID) CFO disclosed

Rhea-AI Filing Summary

RAPID MICRO BIOSYSTEMS, INC. Chief Financial Officer Sean M. Wirtjes reported an automatic sale of 7,480 shares of Class A Common Stock. The shares were sold at an average price of $4.3181 per share to cover tax obligations arising from the vesting of restricted stock units. After this tax-related sale, he directly holds 556,194 shares, indicating he retains a substantial equity position in the company.

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

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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^*

WIRTJES SEAN M

(Last) (First) (Middle)

C/O RAPID MICRO BIOSYSTEMS, INC.

25 HARTWELL AVENUE

(Street)

LEXINGTON MA 02421

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
RAPID MICRO BIOSYSTEMS, INC. [ RPID ]

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

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	CHIEF FINANCIAL OFFICER

3. Date of Earliest Transaction (Month/Day/Year)
03/11/2026

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

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

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

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	03/11/2026		S		7,480(1)	D	$4.3181	556,194	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 the automatic sale of stock to cover the associated tax obligations with the vesting of restricted stock units.

Remarks:

	/s/ Sean M. Wirtjes	03/12/2026
	** 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.

FAQ

What insider transaction did RAPID MICRO BIOSYSTEMS (RPID) report for its CFO?

RAPID MICRO BIOSYSTEMS reported that CFO Sean M. Wirtjes automatically sold 7,480 shares of Class A Common Stock. The transaction was an open-market sale used solely to cover tax obligations tied to vesting restricted stock units, rather than a discretionary portfolio decision.

At what price did the RPID CFO’s tax-related share sale occur?

The CFO’s 7,480 Class A Common Stock shares were sold at an average price of $4.3181 per share. This sale was executed automatically to satisfy tax obligations associated with restricted stock unit vesting, as disclosed in the accompanying footnote to the insider transaction.

How many RPID shares does the CFO hold after this Form 4 transaction?

Following the tax-related sale, CFO Sean M. Wirtjes directly holds 556,194 shares of RAPID MICRO BIOSYSTEMS Class A Common Stock. This indicates the reported transaction involved only a small portion of his total disclosed holdings, with the majority of his equity stake remaining intact.

Was the RPID CFO’s Form 4 sale a discretionary stock sale?

The filing specifies the sale was automatic to cover tax obligations from restricted stock unit vesting. This means it was a mechanistic transaction driven by tax requirements, rather than a discretionary decision to reduce the CFO’s investment exposure to RAPID MICRO BIOSYSTEMS shares.

What does the footnote in the RPID Form 4 say about the CFO’s sale?

The footnote explains that the reported shares represent an automatic sale of stock to cover associated tax obligations upon restricted stock unit vesting. This clarifies the sale’s purpose as tax withholding, providing important context for interpreting the CFO’s reported open-market transaction.