Material Agreement (Form 8-K)

Item 1.01. Entry into a Material Definitive Agreement.

On March 18, 2026, REGENXBIO Inc. (the "Company") entered into a Settlement and Release Agreement (the "Settlement Agreement") with GlaxoSmithKline LLC ("GSK") to resolve non-binding mediation related to the License Agreement dated March 6, 2009, as amended on April 15, 2009, between GSK and the Company (as amended, the "GSK-REGENXBIO Sublicense").

As previously disclosed, the Company was notified of a dispute with GSK over the amount of sublicense fees paid by the Company to GSK under the GSK-REGENXBIO Sublicense. Pursuant to the terms of the Settlement Agreement, the Company will make a payment of $10.0 million to GSK within three business days of the Settlement Agreement effective date for alleged underpayment of sublicense fees on amounts received by the Company from sublicensees, including royalties.

The Settlement Agreement includes mutual releases of (a) all past claims arising out of or related to the GSK-REGENXBIO Sublicense and (b) certain specified types of future claims arising out of or related to the GSK-REGENXBIO Sublicense. The Company will continue to pay GSK amounts received from sublicensees pursuant to existing sublicense agreements, utilizing the Company's existing allocation methodology.

The foregoing description of the terms of the Settlement Agreement does not purport to be complete and is qualified in its entirety by the full text of such agreement. The Company intends to file a copy of the Settlement Agreement with its Quarterly Report on Form 10-Q for the quarter ending March 31, 2026.