POS AM 1 gbio-20260209xposam.htm POS AM

As filed with the Securities and Exchange Commission on February 9, 2026

Registration No. 333-281335

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

POST-EFFECTIVE AMENDMENT NO. 1 TO FORM S-3 REGISTRATION
STATEMENT NO. 333-281335

UNDER

THE SECURITIES ACT OF 1933

Generation Bio Co.

(Exact name of registrant as specified in its charter)

Delaware		81-4301284
(State or other jurisdiction of incorporation or organization)		(I.R.S. Employer Identification Number)

301 Binney Street

Cambridge, Massachusetts 02142

(617) 655-7500

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Owen Hughes

XOMA Royalty Corporation

2200 Powell Street, Suite 310

Emeryville, California 94608

(510) 204-7200

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Ryan A. Murr

Branden C. Berns

Gibson, Dunn & Crutcher LLP

One Embarcadero Center, Suite 2600

San Francisco, CA 94111

(415) 393-8200

Approximate date of commencement of proposed sale to the public: Not applicable

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box: ☐

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box: ☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. ☐

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer	☐	Accelerated filer	☐
Non-accelerated filer	☒	Smaller reporting company	☒
		Emerging growth company	☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

DEREGISTRATION OF SECURITIES

This Post-Effective Amendment (the “Post-Effective Amendment”) filed by Generation Bio Co. (the “Registrant”) relates to Registration Statement No. 333-281335 (the “Registration Statement”), filed with the U.S. Securities and Exchange Commission (the “SEC”) on August 7, 2024, which became effective on August 15, 2024, registering the offering, issuance and sale by the Registrant of up to $600,000,000 of the Registrant’s common stock, $0.0001 par value per share (“Common Stock”), preferred stock, debt securities, warrants and units consisting of some or all of these securities, including the offering and sale by the Registrant of up to $237,000,000 of Common Stock pursuant to the Sales Agreement, dated August 7, 2024, by and between the Registrant and TD Securities (USA), LLC, as sales agent.

On February 9, 2026, pursuant to that certain Agreement and Plan of Merger, dated as of December 15, 2025 (the “Merger Agreement”), by and among the Registrant, XOMA Royalty Corporation, a Nevada corporation (“Parent”), and XRA 7 Corp., a Delaware corporation and a wholly-owned subsidiary of Parent (“Merger Sub”), Merger Sub merged with and into the Registrant, with the Registrant surviving as a wholly-owned subsidiary of Parent. As a result of the transactions contemplated by the Merger Agreement, the Registrant has terminated all offerings of its securities pursuant to the Registration Statement. The Registrant, by filing this Post-Effective Amendment, hereby terminates the effectiveness of the Registration Statement and removes from registration any and all securities registered but unsold under the Registration Statement as of the date hereof. The Registration Statement is hereby amended, as appropriate, to reflect the deregistration of such securities. After giving effect to this Post-Effective Amendment, there will be no securities registered by the Registrant pursuant to the Registration Statement.

SIGNATURE

Pursuant to the requirements of the Securities Act of 1933, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this Post-Effective Amendment to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Emeryville, State of California, on February 9, 2026.

	GENERATION BIO CO.

	By:	/s/ Owen Hughes
	Name:	Owen Hughes
	Title:	President, Treasurer and Secretary

No other person is required to sign this Post-Effective Amendment in reliance upon Rule 478 under the Securities Act of 1933, as amended.