[SCHEDULE 13G] REPLIGEN CORP Passive Investment Disclosure (>5%)

Rhea-AI Filing Summary

FMR LLC and Abigail P. Johnson report a 5.1% beneficial stake in Repligen Corp common stock. As of December 31, 2025, they report beneficial ownership of 2,891,140.17 shares, representing 5.1% of the outstanding common stock. FMR LLC has sole voting power over 2,876,401.55 shares and sole dispositive power over 2,891,140.17 shares, while Abigail P. Johnson has sole dispositive power over the same 2,891,140.17 shares with no voting power. The securities are certified as being held in the ordinary course of business and not for the purpose of changing or influencing control of Repligen. One or more other persons may have rights to dividends or sale proceeds, but no single such interest exceeds five percent of the class.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

REPLIGEN CORP

(Name of Issuer)

COMMON STOCK

(Title of Class of Securities)

759916109

(CUSIP Number)

12/31/2025

(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)

SCHEDULE 13G

CUSIP No. 759916109

1

Names of Reporting Persons

FMR LLC

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 2,876,401.55
6	Shared Voting Power 0.00
7	Sole Dispositive Power 2,891,140.17
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,891,140.17

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)

5.1 %

12

Type of Reporting Person (See Instructions)

HC

SCHEDULE 13G

CUSIP No. 759916109

1

Names of Reporting Persons

Abigail P. Johnson

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

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 2,891,140.17
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,891,140.17

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)

5.1 %

12

Type of Reporting Person (See Instructions)

IN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: REPLIGEN CORP
(b)	Address of issuer's principal executive offices: 41 SEYON STREET,BUILDING 1, SUITE 100,WALTHAM ,MA,USA,02453
Item 2.
(a)	Name of person filing: FMR LLC
(b)	Address or principal business office or, if none, residence: 245 Summer Street, Boston, Massachusetts 02210
(c)	Citizenship: Not applicable
(d)	Title of class of securities: COMMON STOCK
(e)	CUSIP No.: 759916109
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: 2891140.17
(b)	Percent of class: 5.1 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: Please see the responses to Items 5 and 6 on the cover page.
	(ii) Shared power to vote or to direct the vote: 0.00
	(iii) Sole power to dispose or to direct the disposition of: 2891140.17
	(iv) Shared power to dispose or to direct the disposition of: 0.00
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.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. One or more other persons are known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the COMMON STOCK of REPLIGEN CORP. No one other person's interest in the COMMON STOCK of REPLIGEN CORP is more than five percent of the total outstanding COMMON STOCK.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	If a parent holding company has filed this schedule, pursuant to Rule 13d-1(b)(ii)(G), so indicate under Item 3(g) and attach an exhibit stating the identity and the Item 3 classification of the relevant subsidiary. If a parent holding company has filed this schedule pursuant to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the identification of the relevant subsidiary. See attached Exhibit 99.
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11.

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.

FMR LLC

Signature:	Stephanie J. Brown
Name/Title:	Duly authorized under Power of Attorney effective as of January 3, 2023, by and on behalf of FMR LLC and its direct and indirect subsidiaries*
Date:	02/04/2026

Abigail P. Johnson

Signature:	Stephanie J. Brown
Name/Title:	Duly authorized under Power of Attorney effective as of January 26, 2023, by and on behalf of Abigail P. Johnson**
Date:	02/04/2026

Comments accompanying signature: * This power of attorney is incorporated herein by reference to Exhibit 24 to the Schedule 13G filed by FMR LLC on January 10, 2023, accession number: 0000315066-23-000003. ** This power of attorney is incorporated herein by reference to Exhibit 24 to the Schedule 13G filed by FMR LLC on January 31, 2023, accession number: 0000315066-23-000038.

Exhibit Information

Please see Exhibit 99 for 13d-1(k) (1) agreement.

FAQ

What stake does FMR LLC report in Repligen (RGEN)?

FMR LLC reports beneficial ownership of 2,891,140.17 Repligen common shares, representing 5.1% of the class as of December 31, 2025. This makes FMR a significant institutional holder above the 5% disclosure threshold.

How much voting power does FMR LLC have in Repligen (RGEN)?

FMR LLC reports sole voting power over 2,876,401.55 Repligen common shares. It reports no shared voting power, indicating all disclosed voting authority is held solely by FMR LLC for those shares.

What is Abigail P. Johnson’s beneficial ownership in Repligen (RGEN)?

Abigail P. Johnson is reported as a beneficial owner of 2,891,140.17 Repligen common shares, or 5.1% of the class. She has sole dispositive power over these shares but no reported sole or shared voting power.

Are the Repligen (RGEN) shares held to influence control of the company?

The filing certifies the Repligen shares were acquired and are held in the ordinary course of business. It states they were not acquired and are not held to change or influence control of Repligen, except for limited nomination-related activities cited.

Do others have rights to dividends or sale proceeds from Repligen (RGEN) shares?

The filing states one or more other persons may have rights to receive dividends or sale proceeds from the Repligen common stock. However, it clarifies that no single such person’s interest exceeds five percent of the total outstanding common stock.

Why is a Schedule 13G filed for Repligen (RGEN) here?

Schedule 13G is filed because FMR LLC and Abigail P. Johnson beneficially own more than five percent of Repligen’s common stock. They certify the holdings are in the ordinary course of business and not aimed at changing or influencing control of the issuer.