KAISER ALUMINUM CORP

Entry into a Material Definitive Agreement. On April 23, 2025, we and the United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union, AFL-CIO, CLC (formerly known as the United Steelworkers of America, AFL-CIO, CLC) (the "USW") amended and restated the terms of the amended and restated director designation agreement dated September 3, 2021 (the "Agreement"), to extend the term of the Agreement from December 31, 2025 to December 31, 2030 (the "Amendment"). The Amendment was entered into in connection with the renewal and ratification of a labor agreement with members of the USW at our Newark, Ohio and Spokane, Washington facilities.

As with the Agreement, the Amendment provides the USW with the right to designate for nomination the minimum number of candidates necessary to ensure that, assuming such candidates are elected by our stockholders, at least 40% of the members of our Board of Directors immediately following such election of directors who were designated by the USW. The Amendment also provides that we have the ability to increase the size of our Board of Directors from 10 to up to 12 members without increasing the number of candidates that the USW has the right to designate for nomination.

The preceding description of the Amendment is a summary and is qualified in its entirety by the Amendment, which is filed as Exhibit 10.5 hereto and is incorporated herein by reference.

Rule 10b5-1 Trading Arrangements. During the quarter ended March 31, 2025, no director or officer of the Company adopted, modified, orterminated a "Rule 10b5-1 trading arrangement" or "non-Rule 10b5-1 trading arrangement" as each term is defined in Item 408 of Regulation S-K.