pnw-20260904 UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, DC 20549     FORM 8-K     CURRENT REPORT Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Date of report (Date of earliest event reported): September 4, 2026 Commission File Number Exact Name of Registrant as Specified in Charter; State or Other Jurisdiction of Incorporation; Address of Principal Executive Officers, and Zip Code; and Registrant's telephone Number, Including Area Code) IRS Employer Identification No. 1-8962 PINNACLE WEST CAPITAL CORPORATION 86-0512431 (an Arizona corporation) 400 North Fifth Street, P.O. Box 53999 Phoenix Arizona 85072-3999 (602) 250-1000 1-4473 ARIZONA PUBLIC SERVICE COMPANY 86-0011170 (an Arizona corporation) 400 North Fifth Street, P.O. Box 53999 Phoenix Arizona 85072-3999 (602) 250-1000 Not Applicable (Former name or former address, if changed since last report.) Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions: ☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) ☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12) ☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) ☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c)) Securities registered pursuant to Section 12(b) of the Act: Title of each class Trading Symbol(s) Name of each exchange on which registered Common Stock, no par value PNW New York Stock Exchange Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (17 CFR §230.405) or Rule 12b-2 of the Securities Exchange Act of 1934 (17 CFR §240.12b-2). Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ¨ This combined Form 8-K is separately filed or furnished by Pinnacle West Capital Corporation and Arizona Public Service Company. Each registrant is filing or furnishing on its own behalf all of the information contained in this Form 8-K that relates to such registrant and, where required, its subsidiaries. Except as stated in the preceding sentence, neither registrant is filing or furnishing any information that does not relate to such registrant, and therefore makes no representation as to any such information. Item 7.01    Regulation FD Disclosure. Pinnacle West Capital Corporation (“Pinnacle West”) will be participating in various meetings with securities analysts and investors in September 2026 and will be utilizing handouts during those meetings. Copies of the handouts are attached hereto as Exhibit 99.1. Item 9.01    Financial Statements and Exhibits.     (d)    Exhibits Exhibit No. Registrant(s) Description 99.1 Pinnacle West Arizona Public Service Company Pinnacle West handouts for use at meetings in S eptember 2026 104 Pinnacle West Arizona Public Service Company 104 Cover Page Interactive Data File (embedded within the Inline XBRL document) SIGNATURES     Pursuant to the requirements of the Securities Exchange Act of 1934, each registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized. PINNACLE WEST CAPITAL CORPORATION (Registrant) Dated: September 4, 2026 By: /s/ Andrew Cooper Andrew Cooper Senior Vice President and Chief Financial Officer ARIZONA PUBLIC SERVICE COMPANY (Registrant) Dated: September 4, 2026 By: /s/ Andrew Cooper Andrew Cooper Senior Vice President and Chief Financial Officer