Material Agreement, Financial Obligation (Form 8-K)

On September 16, 2025, American Tower Corporation (the "Company") completed a registered public offering of $200.0 million aggregate principal amount of its 4.900% senior unsecured notes due 2030 (the "2030 notes") and $375.0 million aggregate principal amount of its 5.350% senior unsecured notes due 2035 (the "2035 notes" and, together with the 2030 notes, the "Notes"), which resulted in aggregate net proceeds to the Company of approximately $587.8 million, after deducting commissions and estimated expenses. The 2030 notes will be consolidated, form a single series and be fully fungible, with the Company's outstanding $650,000,000 4.900% senior unsecured notes due 2030 issued on March 14, 2025. The 2035 notes will be consolidated, form a single series and be fully fungible, with the Company's outstanding $350,000,000 5.350% senior unsecured notes due 2035 issued on March 14, 2025. The Company intends to use the net proceeds to repay existing indebtedness under its $4.0 billion senior unsecured revolving credit facility and for general corporate purposes.

The Company issued the Notes under an indenture dated as of June 1, 2022 (the "Base Indenture"), as supplemented by a supplemental indenture dated as of March 14, 2025 (the "Supplemental Indenture No. 8" 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 2030 notes will mature on March 15, 2030 and bear interest at a rate of 4.900% per annum. The 2035 notes will mature on March 15, 2035 and bear interest at a rate of 5.350% per annum. Accrued and unpaid interest on the Notes will be payable in U.S. Dollars semi-annually in arrears on March 15 and September 15 of each year, beginning on March 15, 2026. Interest on the Notes will accrue from September 15, 2025 and will be computed on the basis of a 360-dayyear comprised of twelve 30-daymonths. The terms of the Indenture, among other things, limit (a) the Company's ability to merge, consolidate or sell assets and (b) the Company's and its subsidiaries' abilities to incur liens. These covenants are subject to a number of exceptions, including that the Company and its subsidiaries may incur liens on assets, mortgages or other liens securing indebtedness, provided the aggregate amount of indebtedness secured by such liens shall not exceed 3.5x Adjusted EBITDA as defined in the Indenture.

The Company may redeem the Notes at any time, in whole or in part, at its election at the applicable redemption price. If the Company redeems (a) the 2030 notes prior to February 15, 2030 or (b) the 2035 notes prior to December 15, 2034, the Company shall pay a redemption price equal to 100% of the principal amount of the notes being redeemed plus a make-whole premium, together with accrued interest to the redemption date. If the Company redeems (a) the 2030 notes on or after February 15, 2030 or (b) the 2035 notes on or after December 15, 2034, the Company shall pay a redemption price equal to 100% of the principal amount of the notes being redeemed plus accrued interest to the redemption date. In addition, if the Company undergoes a Change of Control and Ratings Decline, each as defined in the Indenture, the Company may be required to repurchase all of the Notes at a purchase price equal to 101% of the principal amount of the Notes, plus accrued and unpaid interest (including additional interest, if any), up to but not including the repurchase date.

The Indenture provides that each of the following is an event of default ("Event of Default"): (i) default for 30 days in payment of any interest due with respect to the Notes; (ii) default in payment of principal or premium, if any, on the Notes when due, at maturity, upon any redemption, by declaration or otherwise; (iii) failure by the Company to comply with covenants in the Indenture or Notes for 90 days after receiving notice; and (iv) certain events of bankruptcy or insolvency with respect to the Company or any of its Significant Subsidiaries. If any Event of Default arising under clause (iv) above occurs, the principal amount and accrued and unpaid interest on all the outstanding Notes will become due and payable immediately without further action or notice. If any other Event of Default occurs and is continuing, the Trustee or the holders of at least 25% in principal amount of the then outstanding Notes may declare the entire principal amount on all the outstanding Notes to be due and payable immediately.

The foregoing is only a summary of certain provisions and is qualified in its entirety by the terms of the Base Indenture, as filed with the Securities and Exchange Commission (the "SEC") on June 1, 2022 as an exhibit to the Company's Registration Statement on Form S-3(No. 333-265348),and the Supplemental Indenture No. 8, as filed with the SEC on March 14, 2025 as an exhibit to the Company's Current Report on Form 8-Kand incorporated by reference herein.

Please refer to the discussion under Item 1.01 above, which is incorporated under this Item 2.03 by reference.