FORM 8-K Washington, D.C. 20549 CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of Report (Date of earliest event reported): January 7, 2026 Frontier Group Holdings, Inc. (Exact name of registrant as specified in its charter) (State or other jurisdiction of incorporation) UNITED STATES SECURITIES AND EXCHANGE COMMISSION ☐ 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 ...