Company Update

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D. C. 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) May 20, 2025 Commission File Number Registrant, State of Incorporation, Address and Telephone Number I.R.S. Employer Identification No. 1-3526 The Southern Company 58-0690070 (A Delaware Corporation) 30 Ivan Allen Jr. Boulevard, N.W . Atlanta , Georgia 30308 ( 404 ) 506-5000 The name and address of the registrant have not changed since the 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: Registrant Title of each class Trading Symbol(s) Name of each exchange on which registered The Southern Company Common Stock, par value $5 per share SO New York Stock Exchange The Southern Company Series 2017B 5.25% Junior Subordinated Notes due 2077 SOJC New York Stock Exchange The Southern Company Series 2020A 4.95% Junior Subordinated Notes due 2080 SOJD New York Stock Exchange The Southern Company Series 2020C 4.20% Junior Subordinated Notes due 2060 SOJE New York Stock Exchange The Southern Company Series 2021B 1.875% Fixed-to-Fixed Reset Rate Junior Subordinated Notes due 2081 SO 81 New York Stock Exchange The Southern Company Series 2025A 6.50% Junior Subordinated Notes due 2085 SOJF 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 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter). 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.   ☐ Item 8.01. Other Events . On May 20, 2025, The Southern Company (the “Company”) issued a press release announcing a proposed offering of $1,250,000,000 aggregate principal amount of convertible senior notes in a private offering to persons reasonably believed to be qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended. In addition, the Company expects to grant the initial purchasers an option to purchase, for settlement within a period of 13 days from, and including, the date the convertible senior notes are first issued, up to an additional $200,000,000 aggregate principal amount of convertible senior notes. A copy of the press release is attached hereto as Exhibit 99.1 and incorporated by reference herein. Item 9.01. Financial Statements and Exhibits. (d) Exhibits. 99.1 Press Release issued by the Company on May 20, 2025 announcing a proposed offering of convertible senior notes . 104 Cover Page Interactive Data File – The cover page iXBRL tags are embedded within the inline XBRL document. SIGNATURE 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 hereunto duly authorized. Date:   May 20, 2025 THE SOUTHERN COMPANY By /s/Melissa K. Caen Melissa K. Caen Assistant Secretary 2