SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 1)

Generation Bio Co.

(Name of Issuer)

Common Stock, $0.0001 Par Value

(Title of Class of Securities)

37148K209

(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.

37148K209

Names of Reporting Persons

Renaissance Technologies LLC

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

(a)

(b)

Sec Use Only

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 287,614.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 287,614.00
8	Shared Dispositive Power 0.00

Aggregate Amount Beneficially Owned by Each Reporting Person

287,614.00

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

Checkbox not checked

Percent of class represented by amount in row (9)

4.27 %

Type of Reporting Person (See Instructions)

SCHEDULE 13G

CUSIP No.

37148K209

Names of Reporting Persons

Renaissance Technologies Holdings Corporation

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

(a)

(b)

Sec Use Only

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 287,614.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 287,614.00
8	Shared Dispositive Power 0.00

Aggregate Amount Beneficially Owned by Each Reporting Person

287,614.00

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

Checkbox not checked

Percent of class represented by amount in row (9)

4.27 %

Type of Reporting Person (See Instructions)

SCHEDULE 13G

Item 1.

(a)

Name of issuer:

Generation Bio Co.

(b)

Address of issuer's principal executive offices:

301 BINNEY STREET, CAMBRIDGE, MA 02142

Item 2.

(a)

Name of person filing:

This Schedule 13G is being filed by Renaissance Technologies LLC ("RTC") and Renaissance Technologies Holdings Corporation ("RTHC").

(b)

Address or principal business office or, if none, residence:

800 Third Avenue New York, New York 10022

(c)

Citizenship:

RTC is a Delaware limited liability company, and RTHC is a Delaware corporation.

(d)

Title of class of securities:

Common Stock, $0.0001 Par Value

(e)

CUSIP No.:

37148K209

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:

287614

(b)

Percent of class:

4.27 %

(c)

Number of shares as to which the person has:

(i) Sole power to vote or to direct the vote:

287614

(ii) Shared power to vote or to direct the vote:

(iii) Sole power to dispose or to direct the disposition of:

287614

(iv) Shared power to dispose or to direct the disposition of:

Item 5.

Ownership of 5 Percent or Less of a Class.

Ownership of 5 percent or less of a class

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.

Certain funds managed by RTC have the right to receive dividends and proceeds from the sale of the securities which are the subject of this report.

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:

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.

Renaissance Technologies LLC

Signature:	Brian Felczak
Name/Title:	Chief Financial Officer
Date:	02/12/2026

Renaissance Technologies Holdings Corporation

Signature:	Brian Felczak
Name/Title:	Vice President
Date:	02/12/2026

Exhibit Information

In accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended, each of the undersigned agrees to the filing on behalf of each of a Statement on Schedule 13G, and all amendments thereto, with respect to the shares of Common Stock, $0.0001 Par Value of Generation Bio Co.

Amendment: SEC Form SCHEDULE 13G/A filed by Generation Bio Co.