Statement of Changes in Beneficial Ownership (Form 4)

FORM 4 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 that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES 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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1. Name and Address of Reporting Person * Spignesi Robert G. Jr. 2. Issuer Name and Ticker or Trading Symbol RAPID MICRO BIOSYSTEMS, INC. [RPID] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) PRESIDENT AND CEO (Last) (First) (Middle) C/O RAPID MICRO BIOSYSTEMS, INC., 25 HARTWELL AVENUE 3. Date of Earliest Transaction (Month/Day/Year) 10/17/2025 (Street) LEXINGTON, MA 02421 4. If Amendment, Date 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 (City) (State) (Zip) 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 10/17/2025 M 3,400 A $0.75 973,950 D Class A Common Stock 10/17/2025 F 2,072(1) D $3.08 971,878 D Class A Common Stock 10/17/2025 M 7,833 A $0.75 979,711 D Class A Common Stock 10/17/2025 F 4,774(2) D $3.08 974,937 D

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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 Underlying Securities (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 of Derivative Security: 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

Stock Option (Right to Buy)

$0.75

10/17/2025

M

3,400

(3)

10/22/2025

Class A Common Stock

3,400

$ 0

0

D

Stock Option (Right to Buy)

$0.75

10/17/2025

M

7,833

(3)

10/22/2025

Class A Common Stock

7,833

$ 0

0

D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Spignesi Robert G. Jr. C/O RAPID MICRO BIOSYSTEMS, INC. 25 HARTWELL AVENUE LEXINGTON, MA 02421	X		PRESIDENT AND CEO

Signatures

/s/ Sean M. Wirtjes, Attorney-in-Fact for Robert G. Spignesi, Jr.		10/21/2025
**Signature of Reporting Person		Date

Explanation of Responses:

*	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).
(1)	Represents a "net exercise" of outstanding stock options. The reporting person received 1,328 shares of common stock on net exercise of option to purchase 3,400 shares of common stock. The Company withheld 2,072 shares of common stock underlying the option for payment of the exercise price and tax withholdings, using the closing stock price on October 17, 2025 of $3.08, pursuant to the terms of the 2010 Stock Option and Grant Plan.
(2)	Represents a "net exercise" of outstanding stock options. The reporting person received 3,059 shares of common stock on net exercise of option to purchase 7,833 shares of common stock. The Company withheld 4,774 shares of common stock underlying the option for payment of the exercise price and tax withholdings, using the closing stock price on October 17, 2025 of $3.08, pursuant to the terms of the 2010 Stock Option and Grant Plan.
(3)	The option is fully vested and exercisable.

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