(AMT)

Role: President and CEO, Director
Signature: /s/ Marina A. Breed, as attorney-in-fact
Issuer symbol: AMT
Transactions as of: 04 Mar 2026
Net transactions value: -$6,309,967
Form type: 4
Filing time: 06 Mar 2026, 16:23:06 UTC
Previous filing: 27 Feb 2026
Next filing: 12 Mar 2026
SEC: View on sec.gov

Reporting Owners (1)

Name	Relationship	Address	Signature	Signature date	CIK
Vondran Steven O	President and CEO, Director	222 BERKELEY STREET, BOSTON	/s/ Marina A. Breed, as attorney-in-fact	06 Mar 2026	0001749304

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
transaction	AMT	Common Stock	Options Exercise		+33,482	+32%	$94.71^*	138,856	04 Mar 2026	Direct
transaction	AMT	Common Stock	Sale	$2,834,284	-15,084	-11%	$187.90	123,772	04 Mar 2026	Direct	F1, F2
transaction	AMT	Common Stock	Sale	$3,139,132	-16,625	-13%	$188.82	107,147	04 Mar 2026	Direct	F1, F3
transaction	AMT	Common Stock	Sale	$336,551	-1,773	-1.7%	$189.82	105,374	04 Mar 2026	Direct	F1, F4

Derivative Securities (e.g., puts, calls, warrants, options, convertible securities)

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Underlying Class	Amount	Exercise Price	Ownership	Footnotes
transaction	AMT	Option to Purchase Common Stock	Options Exercise		-33,482	-100%	$0.000000^*	0	04 Mar 2026	Common Stock	33,482	$94.71	Direct	F5

* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Buy Plan / Sale Plan: These are also open market purchases/sales of shares, but in this case the transaction is part of a trading plan. Rule 10b5-1 allows insiders to setup a trading plan to buy/sell stocks over a certain period of time. Since the purchases/sales are predetermined, this protects the insiders from violating insider trading law.

Transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c).

Explanation of Responses:

Id	Content
F1	The sales reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on May 6, 2025.
F2	Represents the weighted average price of shares sold in multiple same-day transactions at prices ranging from $187.31 to $188.30 per share.
F3	Represents the weighted average price of shares sold in multiple same-day transactions at prices ranging from $188.31 to $189.30 per share.
F4	Represents the weighted average price of shares sold in multiple same-day transactions at prices ranging from $189.58 to $190.09 per share.
F5	This option was granted pursuant to the 2007 Equity Incentive Plan, as amended, and is exercisable in 25% cumulative annual increments beginning March 10, 2017.