Generation Bio (GBIO) ends $600M, $237M ATM shelf after merger

Rhea-AI Filing Summary

Generation Bio Co. filed a post-effective amendment to its Form S-3 shelf registration to formally end a prior securities program after being acquired. The original shelf had registered up to $600,000,000 of common stock, preferred stock, debt securities, warrants and units, including up to $237,000,000 of common stock under a sales agreement with TD Securities (USA), LLC.

On February 9, 2026, XRA 7 Corp., a wholly owned subsidiary of XOMA Royalty Corporation, merged with and into Generation Bio, leaving Generation Bio as a wholly owned subsidiary of XOMA Royalty Corporation. Because of this merger, Generation Bio terminated all offerings under the shelf registration and, through this amendment, deregistered all securities that had been registered but remained unsold. After this change, no securities remain registered under that S-3 registration statement.

Insights

Equity capital markets analyst

Generation Bio’s S-3 shelf is shut down following its acquisition by XOMA Royalty Corporation.

Generation Bio previously maintained a Form S-3 shelf registration covering up to $600,000,000 of securities, including up to $237,000,000 of common stock under a sales agreement with TD Securities (USA), LLC. This gave the company flexibility to issue equity and other securities over time.

After the merger effective on February 9, 2026, where XRA 7 Corp. merged into Generation Bio and the company became a wholly owned subsidiary of XOMA Royalty Corporation, public offerings under that shelf ceased. The post-effective amendment now terminates the registration statement and removes any unsold securities from registration, aligning the capital markets structure with Generation Bio’s new status as a subsidiary rather than an independent issuer.

The filing is largely administrative from a capital markets perspective. It confirms there is no remaining shelf capacity for future offerings under Registration No. 333-281335, and that any future capital raising for the business would occur at the parent or through new registration arrangements disclosed in subsequent filings.

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

Registration No. 333-281335

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

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

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UNDER

THE SECURITIES ACT OF 1933

Generation Bio Co.

(Exact name of registrant as specified in its charter)

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

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301 Binney Street

Cambridge, Massachusetts 02142

(617) 655-7500

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(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

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

Copies to:

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Ryan A. Murr

Branden C. Berns

Gibson, Dunn & Crutcher LLP

One Embarcadero Center, Suite 2600

San Francisco, CA 94111

(415) 393-8200

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

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

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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: ☐

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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. ☐

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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. ☐

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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. ☐

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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. ☐

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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.

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

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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. ☐

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DEREGISTRATION OF SECURITIES

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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.

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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.

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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.

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​	GENERATION BIO CO.
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​	By:	/s/ Owen Hughes
​	Name:	Owen Hughes
​	Title:	President, Treasurer and Secretary

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

FAQ

What did Generation Bio Co. (GBIO) change in this post-effective amendment?

Generation Bio Co. terminated the effectiveness of its Form S-3 shelf registration statement and deregistered all securities that were registered but unsold. This follows its merger into a wholly owned subsidiary of XOMA Royalty Corporation, ending future offerings under that specific registration.

How large was Generation Bio Co.’s prior S-3 shelf registration?

Generation Bio’s S-3 shelf had registered up to $600,000,000 of securities, including common stock, preferred stock, debt securities, warrants and units. It also covered up to $237,000,000 of common stock issuable under a sales agreement with TD Securities (USA), LLC as sales agent.

Why did Generation Bio Co. deregister the securities under Registration No. 333-281335?

Generation Bio deregistered the securities because, after its merger with XRA 7 Corp., it became a wholly owned subsidiary of XOMA Royalty Corporation. As a result, it terminated all offerings under the S-3 shelf and removed any securities that remained registered but unsold under that statement.

What merger led to Generation Bio Co. ending its S-3 offerings?

On February 9, 2026, XRA 7 Corp., a Delaware corporation and wholly owned subsidiary of XOMA Royalty Corporation, merged with and into Generation Bio Co. Under the Agreement and Plan of Merger dated December 15, 2025, Generation Bio survived as a wholly owned subsidiary of XOMA Royalty Corporation.

Does Generation Bio Co. still have securities registered for sale after this amendment?

After this post-effective amendment, Generation Bio Co. states there will be no securities registered by the company under Registration Statement No. 333-281335. All securities that had been registered but were unsold under that S-3 shelf have been removed from registration.

Who signed the post-effective amendment for Generation Bio Co.?

The amendment was signed on behalf of Generation Bio Co. by Owen Hughes, identified as President, Treasurer and Secretary. The company relied on Rule 478 under the Securities Act, which allowed no other person to sign this particular post-effective amendment filing.