TransAlta Corporation - Second Supplemental Indenture

This filing details a Second Supplemental Indenture between TransAlta Corporation and The Bank of New York Mellon, as Trustee, dated December 22, 2025. This indenture supplements the original Indenture dated June 25, 2002, to establish a new series of securities: US$400,000,000 aggregate principal amount of 5.875% Senior Notes due 2034. The indenture outlines terms for the new securities, including their designation, form, transferability, interest rate, maturity, redemption options, and provisions related to a Change of Control Triggering Event. It also details amendments to the original indenture, such as updating the Company's principal executive office address and revising covenants and default provisions to apply specifically to this new series of notes. The document specifies governing law as the State of New York and includes standard provisions regarding the Trustee's role and responsibilities.