TransAlta (TAC) adds Second Supplemental Indenture to Form F-10

Rhea-AI Filing Summary

TransAlta Corporation filed a Form 6-K as a foreign private issuer for December 2025. The filing states that Exhibit 99.1, a Second Supplemental Indenture dated December 22, 2025, is incorporated by reference into TransAlta’s existing Form F-10 shelf registration statement.

Form 6-K: How Foreign Companies Report to the SEC →

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of December 2025

Commission File Number: 001-15214

TransAlta Corporation

(Translation of registrant’s name into English)

Suite 1400, 1100 - 1st Street S.E., Calgary, Alberta, T2G 1B1

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F ☐   Form 40-F ☒

INCORPORATION BY REFERENCE

Exhibit 99.1 of this Form 6-K is incorporated by reference as an additional exhibit to the registrant’s Registration Statement on Form F-10 (File No. 333-292019).

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

						TransAlta Corporation
						(Registrant)
Date: December 22, 2025						/s/ Kelly Galloway
						Kelly Galloway
						Corporate Secretary

EXHIBIT INDEX

Exhibit Number		Description
99.1		Second Supplemental Indenture, dated December 22, 2025

FAQ

What does TransAlta (TAC) report in this December 2025 Form 6-K?

TransAlta’s Form 6-K records the filing of a Second Supplemental Indenture as Exhibit 99.1. This exhibit is incorporated by reference into its Form F-10 shelf registration statement, updating the legal documentation that supports potential future securities offerings under that registration.

What is Exhibit 99.1 in TransAlta’s (TAC) December 2025 Form 6-K?

Exhibit 99.1 is a Second Supplemental Indenture dated December 22, 2025. It is attached to the Form 6-K and incorporated by reference into TransAlta’s Form F-10 registration statement, modifying or supplementing existing indenture terms that support registered securities.

How does this Form 6-K affect TransAlta’s (TAC) Form F-10 registration?

The Form 6-K expressly incorporates Exhibit 99.1 into TransAlta’s Form F-10 registration statement. This means the Second Supplemental Indenture becomes part of the legal framework governing securities that may be issued under that Canadian MJDS shelf registration.

Who signed TransAlta’s (TAC) December 22, 2025 Form 6-K?

The Form 6-K was signed on behalf of TransAlta Corporation by Kelly Galloway as Corporate Secretary on December 22, 2025. This signature confirms the company has duly authorized the submission of the report and the attached supplemental indenture exhibit.

Does the TransAlta (TAC) December 2025 Form 6-K include financial results?

The described Form 6-K does not present financial results. It focuses on corporate legal documentation by filing a Second Supplemental Indenture as Exhibit 99.1 and incorporating that document into the company’s existing Form F-10 shelf registration statement.