Rapid Micro Biosystems (RPID) major holder Bain updates Schedule 13G/A stake

Rhea-AI Filing Summary

Bain Capital Life Sciences–affiliated funds report their ownership in Rapid Micro Biosystems, Inc. Class A common stock. As of June 30, 2026, Bain Capital Life Sciences Fund, L.P. beneficially owned 7,651,369 shares, representing approximately 16.8% of outstanding Class A shares, and BCIP Life Sciences Associates, LP beneficially owned 783,191 shares, representing approximately 1.7% of outstanding shares.

BCLS Investco, LP holds a Pre-Funded Warrant, a Series A Warrant and a Series B Warrant, each exercisable for up to 1,463,000 Class A shares, but is contractually prohibited from exercising any of these if doing so would cause it and affiliated entities to own more than 9.99% of outstanding Class A shares. Based on Rule 13d-3, these warrants are not deemed beneficially owned. The ownership percentages are calculated from 45,660,027 Class A shares outstanding as of July 31, 2026.

Key Figures

BCLS Fund I shares: 7,651,369 shares BCLS Fund I ownership: 16.8% BCIPLS shares: 783,191 shares +5 more

8 metrics

BCLS Fund I shares 7,651,369 shares Class A common stock beneficially owned as of June 30, 2026

BCLS Fund I ownership 16.8% Percentage of Class A common stock outstanding as of June 30, 2026

BCIPLS shares 783,191 shares Class A common stock beneficially owned as of June 30, 2026

BCIPLS ownership 1.7% Percentage of Class A common stock outstanding as of June 30, 2026

Shares outstanding 45,660,027 shares Class A shares outstanding as of July 31, 2026

Pre-Funded Warrant size 1,463,000 shares Maximum Class A shares issuable under Pre-Funded Warrant held by BCLS Investco, LP

Series A Warrant size 1,463,000 shares Maximum Class A shares issuable under Series A Warrant held by BCLS Investco, LP

Beneficial ownership cap 9.99% Maximum collective beneficial ownership allowed upon warrant exercise

Key Terms

Pre-Funded Warrant, Series A Warrant, Series B Warrant, beneficially own, +2 more

6 terms

Pre-Funded Warrant financial

"held a Pre-Funded Warrant to purchase up to 1,463,000 shares of Class A Common Stock"

A pre-funded warrant is a financial instrument that gives the holder the right to buy shares of a company's stock at a set price, with most of the purchase cost already paid upfront. It functions like a nearly fully paid option, allowing investors to secure shares quickly while minimizing the amount of additional money they need to invest later. This helps investors gain ownership rights efficiently, often used to avoid certain regulatory restrictions or to prepare for future stock purchases.

Series A Warrant financial

"a Series A Warrant to purchase up to 1,463,000 shares of Class A Common Stock"

A Series A warrant is a contract issued alongside a company’s early funding round that gives the holder the right to buy a set number of shares later at a fixed price. Think of it like a coupon that lets an investor purchase stock at today’s agreed price even if the company’s value rises; it can boost potential upside for the warrant holder and create dilution for existing shareholders, so investors watch them when assessing ownership and future share value.

Series B Warrant financial

"a Series B Warrant to purchase up to 1,463,000 shares of Class A Common Stock"

A Series B warrant is a tradable right issued alongside a Series B funding round that lets its holder buy a specified number of company shares at a fixed price for a set period. It matters to investors because exercising the warrant increases the total shares outstanding (dilution) and can be a cheap way to gain ownership if the company’s value rises — think of it like a coupon to buy stock later at today’s price.

beneficially own financial

"would collectively beneficially own more than 9.99% of the total number of shares"

Beneficially own means having the economic rights and risks of a security—such as the right to receive dividends, sell the shares, or profit from price changes—whether or not your name appears on the official share register. Think of it like renting a car: you use it and reap the benefits even if the title lists someone else. Investors care because beneficial ownership determines who truly controls value, must be disclosed under securities rules, and can signal potential influence or trading activity that affects a stock’s price.

Rule 13d-3 regulatory

"Accordingly, pursuant to Rule 13d-3 of the Act and the relationships described herein"

Rule 13d-3 defines who is treated as the beneficial owner of a company’s shares for U.S. securities disclosure rules — essentially anyone who has the power to vote or direct how shares are voted, or the power to buy or sell them, even if they don’t hold the certificates. For investors this matters because crossing certain ownership thresholds triggers public filing and disclosure obligations and signals potential control or influence, much like having the keys to a car implies you can drive it even if it’s registered to someone else.

Schedule 13G regulatory

"agreed to file this jointly in accordance with the provisions of Rule 13d-1(k)(1)"

A Schedule 13G is a formal document that investors file with the government when they acquire a large ownership stake in a company, usually for investment purposes rather than control. It helps keep the public informed about who owns significant parts of a company's shares, which can influence how the company is managed and how investors make decisions. Filing this schedule is important for transparency and understanding the ownership landscape of publicly traded companies.

FAQ

How much of Rapid Micro Biosystems (RPID) does Bain Capital Life Sciences Fund own?

Bain Capital Life Sciences Fund, L.P. beneficially owned 7,651,369 shares of Rapid Micro Biosystems Class A common stock, representing approximately 16.8% of the Class A shares outstanding as of June 30, 2026.

What is BCIP Life Sciences Associates LP’s stake in Rapid Micro Biosystems (RPID)?

BCIP Life Sciences Associates, LP held 783,191 shares of Rapid Micro Biosystems Class A common stock, representing approximately 1.7% of the outstanding Class A shares, based on 45,660,027 shares outstanding as of July 31, 2026.

What warrant positions related to Rapid Micro Biosystems (RPID) does BCLS Investco, LP hold?

BCLS Investco, LP holds a Pre-Funded Warrant, a Series A Warrant and a Series B Warrant, each exercisable for up to 1,463,000 Rapid Micro Biosystems Class A shares, subject to a 9.99% beneficial ownership cap.

Why are BCLS Investco LP’s warrants in Rapid Micro Biosystems (RPID) not counted as beneficial ownership?

Because BCLS Investco, LP cannot exercise its warrants if doing so would cause it and affiliates to own over 9.99% of Rapid Micro Biosystems Class A shares, the position is not deemed beneficial ownership under Rule 13d-3.

What share count did Bain Capital Life Sciences use to calculate its percentage ownership of Rapid Micro Biosystems (RPID)?

The reported ownership percentages are based on 45,660,027 Rapid Micro Biosystems Class A common shares outstanding as of July 31, 2026, as reported in the company’s Quarterly Report for the quarter ended June 30, 2026.

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Available on EDGAR 08/14/2026 - 07:00 AM Accepted by SEC EDGAR 08/14/2026 - 07:00 AM Learn about SEC filing dates

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)

Rapid Micro Biosystems, Inc.

(Name of Issuer)

Class A Common Stock, par value $0.01 per share

(Title of Class of Securities)

75340L104

(CUSIP Number)

06/30/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 75340L104

1

Names of Reporting Persons

Bain Capital Life Sciences Fund, L.P.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 7,651,369.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 7,651,369.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

7,651,369.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

16.76 %

12

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13G

CUSIP Number(s): 75340L104

1

Names of Reporting Persons

BCIP Life Sciences Associates, LP

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 783,191.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 783,191.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

783,191.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

1.72 %

12

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Rapid Micro Biosystems, Inc.
(b)	Address of issuer's principal executive offices: 25 Hartwell Avenue, Lexington, Massachusetts 02421
Item 2.
(a)	Name of person filing: This Schedule 13G is being filed jointly by Bain Capital Life Sciences Fund, L.P., a Cayman Islands exempted limited partnership ("BCLS Fund I"), and BCIP Life Sciences Associates, LP, a Delaware limited partnership ("BCIPLS" and, together with BCLS Fund I, the "Reporting Persons"). Bain Capital Life Sciences Investors, LLC, a Delaware limited liability company ("BCLSI"), is the general partner of Bain Capital Life Sciences Partners, LP, a Cayman Islands exempted limited partnership ("BCLSP"), which is the general partner of BCLS Fund I. Boylston Coinvestors, LLC, a Delaware limited liability company ("Boylston" and, together with the Reporting Persons, BCLSI and BCLSP, the "Bain Capital Life Sciences Entities"), is the general partner of BCIPLS. BCLSI governs the investment strategy and decision-making process with respect to investments held by BCIPLS. As a result, BCLSI may be deemed to share voting and dispositive power with respect to the securities held by the Reporting Persons. The Reporting Persons have entered into a Joint Filing Agreement, dated August 14, 2026, pursuant to which the Reporting Persons have agreed to file this Schedule 13G jointly in accordance with the provisions of Rule 13d-1(k)(1) promulgated under the Act.
(b)	Address or principal business office or, if none, residence: The principal business address for each of the Bain Capital Life Sciences Entities is 200 Clarendon Street, Boston, Massachusetts 02116.
(c)	Citizenship: See Item 2(a) hereof.
(d)	Title of class of securities: Class A Common Stock, par value $0.01 per share
(e)	CUSIP No.: 75340L104
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: As of the close of business on June 30, 2026, (i) BCLS Fund I held 7,651,369 shares of Class A Common Stock, representing approximately 16.8% of the outstanding shares of Class A Common Stock, (ii) BCIPLS held 783,191 shares of Class A Common Stock, representing approximately 1.7% of the outstanding shares of Class A Common Stock, and (iii) BCLS Investco, LP, whose ultimate general partner is BCLSI, held a Pre-Funded Warrant to purchase up to 1,463,000 shares of Class A Common Stock, a Series A Warrant to purchase up to 1,463,000 shares of Class A Common Stock (or pre-funded warrants in lieu thereof), and a Series B Warrant to purchase up to 1,463,000 shares of Class A Common Stock (or pre-funded warrants in lieu thereof). BCLS Investco, LP is prohibited from exercising the Pre-Funded Warrant, Series A Warrant, or Series B Warrant if, as a result of such exercise, BCLS Investco, LP, together with its affiliates (including the Reporting Persons), would collectively beneficially own more than 9.99% of the total number of shares of Class A Common Stock then issued and outstanding immediately after giving effect to the exercise. Accordingly, pursuant to Rule 13d-3 of the Act and the relationships described herein, BCLS Investco, LP is not deeemed to beneficially own any shares of Class A Common Stock. The calculation of beneficial ownership is based on 45,660,027 shares of Class A Common Stock outstanding as of July 31, 2026, as reported by the Issuer in its Quarterly Report on Form 10-Q for the quarter ended June 30, 2026, filed with the Securities and Exchange Commission on August 7, 2026.
(b)	Percent of class: See Item 4(a) hereof.
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 0
	(ii) Shared power to vote or to direct the vote: See Item 4(a) hereof.
	(iii) Sole power to dispose or to direct the disposition of: 0
	(iv) Shared power to dispose or to direct the disposition of: See Item 4(a) hereof.
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	Not Applicable
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.	Certifications:
	Not Applicable

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.

Bain Capital Life Sciences Fund, L.P.

Signature:	/s/ Andrew Hack
Name/Title:	Andrew Hack, Partner of Bain Capital Life Sciences Investors, LLC
Date:	08/14/2026

BCIP Life Sciences Associates, LP

Signature:	/s/ Andrew Hack
Name/Title:	Andrew Hack, Authorized Signatory of Boylston Coinvestors, LLC
Date:	08/14/2026