Material Agreement, Financial Obligation (Form 8-K)

On December 5, 2025, American Tower Corporation (the "Company") completed a registered public offering of $850.0 million aggregate principal amount of its 4.700% senior unsecured notes due 2032 (the "Notes"), which resulted in aggregate net proceeds to the Company of approximately $839.5 million, after deducting commissions and estimated expenses. The Company intends to use the net proceeds to repay existing indebtedness under its $4.0 billion senior unsecured revolving credit facility, as amended and restated in December 2021, as further amended.

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 December 5, 2025 (the "Supplemental Indenture No. 1" 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 Notes will mature on December 15, 2032 and bear interest at a rate of 4.700% per annum. Accrued and unpaid interest on the Notes will be payable in U.S. Dollars semi-annually in arrears on June 15 and December 15 of each year, beginning on June 15, 2026. Interest on the Notes will accrue from December 5, 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 the Notes prior to October 15, 2032, 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 the Notes on or after October 15, 2032, 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 on June 2, 2025 as an exhibit to the Company's Registration Statement on Form S-3(No. 333-287714),and the Supplemental Indenture No. 1, a copy of which is filed herewith as Exhibit 4.1, and incorporated by reference herein.

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