AMT: Material agreement · New financial obligation

Item 1.01 Entry into a Material Definitive Agreement. On September 14, 2026, American Tower Corporation (the “Company”) completed a registered public offering of $500.0 million aggregate principal amount of its 5.300% senior unsecured notes due 2031 (the “2031 notes”), $500.0 million aggregate principal amount of its 5.560% senior unsecured notes due 2033 (the “2033 notes”) and $600.0 million aggregate principal amount of its 5.750% senior unsecured notes due 2036 (the “2036 notes” and, collectively with the 2031 notes and the 2033 notes, the “Notes”), which resulted in aggregate net proceeds to the Company of approximately $1,579.9 million, after deducting commissions and estimated expenses. The Company intends to use the net proceeds to repay $600.0 million aggregate principal amount of its 1.450% senior unsecured notes due 2026, to repay existing indebtedness under its $6.0 billion senior unsecured multicurrency revolving credit facility, as amended and restated in December 2021, as further amended, and for general corporate purposes. The Company issued the Notes under an indenture dated as of June 2, 2025 (the “Base Indenture”), as supplemented by a supplemental indenture dated as of September 14, 2026 (the “Supplemental Indenture No. 3” and, together with the Base Indenture, the “Indenture”), each between the Company and U.S. Bank Trust Company, National Association, as trustee (the “Trustee”). The following description of the Indenture is a summary and is qualified in its entirety by reference to the detailed provisions of the Indenture. The 2031 notes will mature on September 15, 2031 and bear interest at a rate of 5.300% per annum. The 2033 notes will mature on September 15, 2033 and bear interest at a rate of 5.560% per annum. The 2036 notes will mature on Sept