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): July 31, 2026

AMEREN CORPORATION

(Exact name of registrant as specified in its charter)

1901 Chouteau Avenue, St. Louis, Missouri 63103

(Address of principal executive offices and Zip Code)

Registrant’s telephone number, including area code: (314) 621-3222

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:

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). ¨

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. ¨

On July 31, 2026, Ameren Corporation (the “Company”) delivered a notice pursuant to Section 3(x) of its Equity Distribution Sales Agreement dated May 12, 2021, as amended and supplemented, including by the First Amendment to Equity Distribution Sales Agreement dated August 7, 2025 (as so amended and supplemented, the “Sales Agreement”), with Barclays Capital Inc., BofA Securities, Inc., Goldman Sachs & Co. LLC, J.P. Morgan Securities LLC, Mizuho Securities USA LLC, Morgan Stanley & Co. LLC, MUFG Securities Americas Inc., RBC Capital Markets, LLC and Wells Fargo Securities, LLC, as sales agents and as forward sellers (in such capacities as applicable, the “Agents” and the “Forward Sellers”), and Bank of America, N.A., Barclays Bank PLC, Goldman Sachs & Co. LLC, JPMorgan Chase Bank, National Association, Mizuho Markets Americas LLC, Morgan Stanley & Co. LLC, MUFG Securities EMEA plc, Royal Bank of Canada and Wells Fargo Bank, National Association, as forward purchasers (the “Forward Purchasers”), increasing by $2,000,000,000 the aggregate gross sales price authorized under the Company’s equity distribution program (the “Program”), pursuant to which the Company, through the Agents or the Forward Sellers, may offer and sell from time to time shares of the Company’s common stock, par value $0.01 per share (the “Common Stock”). After giving effect to such increase, Common Stock with an aggregate gross sales price of up to $2,266,700,000 remains available for issuance under the Program. The Company has no obligation to offer or sell any Common Stock under the Sales Agreement and may at any time suspend offers under the Sales Agreement.

This Current Report on Form 8-K is also being filed to report Exhibit 5.

SIGNATURES

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: August 4, 2026