Note 11. Subsequent Events

On August 3, 2026, the Company entered into the Termination Agreement with CSL Seqirus pursuant to which the Company and CSL Seqirus mutually terminated the CSL Collaboration Agreement, effective as of such date. Under the Termination Agreement, the Company received a one-time cash payment of $12.0 million from CSL Seqirus. In addition, the Company was released from a liability and from repayment of an R&D credit with an aggregate value of approximately $16.0 million.

As a result of the termination, the Company regained strategic control of its vaccine portfolio, including KOSTAIVE® and its vaccine programs for seasonal influenza, pandemic influenza, respiratory syncytial virus (“RSV”) and Epstein-Barr virus (“EBV”), subject to ongoing arrangements with Meiji Seika Pharma (“Meiji”) for the Northern Hemisphere 2026-2027 season, which is expected to end on or around June 30, 2027. Beginning with the Northern Hemisphere 2027–2028 season, the Company expects to work directly with Meiji for KOSTAIVE® activities in Japan.

Arcturus is obligated to pay CSL Seqirus single-digit royalties and revenue-sharing payments on our future commercialization of vaccine products formerly licensed under the CSL Collaboration Agreement and successor products, where certain CSL Seqirus intellectual property is incorporated into such products, subject to agreed terms and conditions and applicable time limitations. With respect to certain of the vaccine products, Arcturus is obligated to pay a percentage of upfront payments received from future licensees up to pre-agreed amounts.

As a result of the termination, the Company expects deferred revenue from CSL Seqirus of approximately $5.2 million associated with remaining performance obligations under the CSL Collaboration Agreement to be recognized during the third quarter of 2026.

In connection with the termination, the parties agreed to dismiss the arbitration and exchanged mutual releases of claims.