Talen Energy Corp

Rule 10b5-1 Trading Plans

During the three months ended March 31, 2026, none of our directors or “officers” (as such term is defined in Rule 16(a)-1(f) under the Exchange Act)adopted orterminated a “Rule 10b5-1 trading agreement” or “non-Rule 10b5-1 trading arrangement” (each as defined in Item 408 of Regulation S-K).

Unsecured Notes due 2031 and 2033. In April 2026, TES issued in private placement transactions not involving a public offering, and each at par: (i) $1.5 billion in aggregate principal amount of 6.125% Senior Unsecured Notes due 2031, with interest payable on May 1 and November 1 of each year, and (ii) $2.5 billion in aggregate principal amount of 6.375% Senior Unsecured Notes due 2033, with interest payable on May 1 and November 1 of each year. We intend to use the net proceeds from the issuance and sale of the Unsecured Notes due 2031 and 2033 to fund the cash portion of the Cornerstone Acquisition and we have used a portion of the net proceeds to redeem the Company’s outstanding Secured Notes. The Unsecured Notes due 2031 were issued under an indenture, dated April 29, 2026 (the “2031 Unsecured Notes Indenture”), by and among TES, the guarantors party thereto and Wilmington Savings Fund Society, FSB, as trustee. The Unsecured Notes due 2033 were issued under an indenture, dated April 29, 2026 (the “2033 Unsecured Notes Indenture”), by and among TES, the guarantors party thereto and Wilmington Savings Fund Society, FSB, as trustee.

The Unsecured Notes due 2031 and 2033 are subject to customary negative covenants, including but not limited to, certain limitations on incurrence of liens and transactions involving the Susquehanna assets, but do not contain any financial covenants. The Unsecured Notes due 2031 and 2033 also contain customary affirmative covenants, events of default, and remedies (including acceleration) and are subject to mandatory redemption provisions in the event that the Cornerstone Acquisition is not completed pursuant to the note purchase agreement. In the event that the Cornerstone Acquisition has not been consummated by January 15, 2027 (or, to the extent such date is automatically extended pursuant to the terms of the Cornerstone Merger Agreement,July 15, 2027), $1.05 billion in aggregate principal amount of the Unsecured Notes due 2031 and $1.75 billion in aggregate principal amount of the Unsecured Notes due 2033 will be redeemed, in each case, at a price equal to 100% of the issue price, plus accrued and unpaid interest.

Secured Notes. In April 2026, TES redeemed in full, the Company’s outstanding Secured Notes in aggregate principal amount of $1.2 billion, using a portion of the net proceeds of the Unsecured Notes due 2031 and 2033. In connection with the redemption, approximately $60 million of expenses are expected to be incurred, primarily consisting of a make-whole payment and derecognition of capitalized deferred finance costs.

Credit Facility Transactions. Also in April 2026, TES undertook the following financing transactions that are expected to become effective concurrently with the closing of the Cornerstone Acquisition: (i) received commitments to increase its existing RCF (including its revolving LC capacity) from $900 million to $1.35 billion; and (ii) received commitments to upsize its existing $1.1 billion LCF to $1.5 billion and extend the maturity from December 2027 to December 2029.

The foregoing description is qualified in its entirety by reference to the full text of the 2031 Unsecured Notes Indenture and the 2033 Unsecured Notes Indenture,and the forms of the Unsecured Notes due 2031 and the Unsecured Notes due 2033, copies of which are filed as Exhibits 4.2, 4.3, 4.4 and 4.5 to this Quarterly Report on Form 10-Q and each of which is incorporated by reference into this Item 5.