X0202 SCHEDULE 13G 0001707921 XXXXXXXX LIVE Common Stock, par value $0.001 per share 06/15/2026 0001622536 Talen Energy Corp 87422Q109 2929 Allen Pkwy, Suite 2200 Houston TX 77019 Rule 13d-1(c) ECP ControlCo, LLC DE 0.00 2399998.00 0.00 2399998.00 2399998.00 N 5.01 OO Limited Liability Company ECP V, LLC DE 0.00 2399998.00 0.00 2399998.00 2399998.00 N 5.01 OO Limited Liability Company ECP V GP Cornerstone DRE, LP DE 0.00 62259.00 0.00 62259.00 62259.00 N 0.1 PN ECP V Cornerstone DRE, LP DE 0.00 371262.00 0.00 371262.00 371262.00 N 0.8 PN ECP V-B Cornerstone DRE, LP DE 0.00 52253.00 0.00 52253.00 52253.00 N 0.1 PN ECP V-C Cornerstone DRE, LP DE 0.00 757539.00 0.00 757539.00 757539.00 N 1.6 PN ECP V-D Cornerstone DRE, LP DE 0.00 1156685.00 0.00 1156685.00 1156685.00 N 2.4 PN Talen Energy Corp 2929 Allen Pkwy, Suite 2200, Houston, TX, 77019 Each of the following is hereinafter individually referred to as a "Reporting Person" and collectively as the "Reporting Persons." This statement is filed on behalf of: ECP ControlCo, LLC ECP V, LLC ECP V GP Cornerstone DRE, LP ECP V Cornerstone DRE, LP ECP V-B Cornerstone DRE, LP ECP V-C Cornerstone DRE, LP ECP V-D Cornerstone DRE, LP The principal business office address for each of the Reporting Persons is c/o ECP ControlCo, LLC, 40 Beechwood Road, Summit, NJ 07901. Each of the Reporting Persons is organized under the laws of the State of Delaware. Y The information contained on the cover pages to this Schedule 13G is incorporated by reference into this Item 4. The ownership information presented herein represents beneficial ownership of Common Stock as of the date of this filing, based upon 47,894,656 shares of Common Stock outstanding as of June 18, 2026, as disclosed in the Issuer's Form S-3 Registration Statement filed with the Securities and Exchange Commission on June 18, 2026. The number of securities reported as beneficially owned herein includes: 62,259 shares of Common Stock held by ECP V GP Cornerstone DRE, LP; 371,262 shares of Common Stock held by ECP V Cornerstone DRE, LP; 52,253 shares of Common Stock held by ECP V-B Cornerstone DRE, LP; 757,539 shares of Common Stock held by ECP V-C Cornerstone DRE, LP; and 1,156,685 shares of Common Stock held by ECP V-D Cornerstone DRE, LP. ECP ControlCo, LLC is the managing member of ECP V, LLC. ECP V, LLC, as a result of its indirect control over each of the following entities, may be deemed to share beneficial ownership of the securities held of record by each of ECP V GP Cornerstone DRE, LP, ECP V Cornerstone DRE, LP, ECP V-B Cornerstone DRE, LP, ECP V-C Cornerstone DRE, LP and ECP V-D Cornerstone DRE, LP. ECP ControlCo, LLC is controlled by its board of managers, which consists of Douglas Kimmelman, Peter Labbat, Tyler Reeder, Rahman D'Argenio, Raoul Hughes and Xavier Robert, all of whom collectively share the power to vote and dispose of the securities beneficially owned by ECP ControlCo, LLC. As a result of the relationships described herein, each of ECP ControlCo, LLC and the individuals named herein may be deemed to share beneficial ownership of the securities that may be deemed to be beneficially owned by ECP V, LLC. Each of them disclaims any such beneficial ownership. See the information contained on the cover pages to this Schedule 13G. See the information contained on the cover pages to this Schedule 13G. See the information contained on the cover pages to this Schedule 13G. See the information contained on the cover pages to this Schedule 13G. See the information contained on the cover pages to this Schedule 13G. Y Y Y Y Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11. Exhibit 99: Joint Filing Agreement. ECP ControlCo, LLC /s/ Jennifer Gray 06/23/2026 ECP V, LLC By: ECP ControlCo, LLC, its managing member, /s/ Jennifer Gray 06/23/2026 ECP V GP Cornerstone DRE, LP By: Cornerstone DRE GP, LLC, its General Partner, /s/ Jennifer Gray 06/23/2026 ECP V Cornerstone DRE, LP By: Cornerstone DRE GP, LLC, its General Partner, /s/ Jennifer Gray 06/23/2026 ECP V-B Cornerstone DRE, LP By: Cornerstone DRE GP, LLC, its General Partner, /s/ Jennifer Gray 06/23/2026 ECP V-C Cornerstone DRE, LP By: Cornerstone DRE GP, LLC, its General Partner, /s/ Jennifer Gray 06/23/2026 ECP V-D Cornerstone DRE, LP By: Cornerstone DRE GP, LLC, its General Partner, /s/ Jennifer Gray 06/23/2026