X0508 4 2026-01-06 0 0001020569 IRON MOUNTAIN INC IRM 0001781215 Matlock Robin C/O IRON MOUNTAIN INCORPORATED 85 NEW HAMPSHIRE AVENUE, SUITE 150 PORTSMOUTH NH 03801 1 0 0 0 0 Phantom Stock 2026-01-06 4 A 0 10.189 84.625 A Common Stock 10.189 10.189 D Pursuant to the Reporting Person's election to participate in the Iron Mountain Incorporated Directors Deferred Compensation Plan (the "Plan"), the shares of phantom stock (the "Phantom Shares") will become payable in shares of Iron Mountain Incorporated common stock ("Common Stock") on various dates selected by the Reporting Person or as otherwise provided in the Plan. Each Phantom Share is the economic equivalent of one share of Common Stock. These shares give effect to dividends paid on Common Stock as if reinvested in Phantom Shares. The price reported in Column 8 is a weighted average price. These shares of Common Stock were acquired in multiple transactions at prices ranging from $84.304 to $84.979, inclusive. The Reporting Person undertakes to provide the Company, any security holder of the Company, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock acquired at each separate price within the ranges set forth in this footnote (3). /s/ Christine Zhang, under Power of Attorney dated May 12, 2025 from Robin Matlock 2026-01-08