Billionaire investor Bill Ackman's Pershing Square has built approximately $2.4 billion positions in both Microsoft (MSFT) and Amazon (AMZN). The fund began accumulating Microsoft shares in February 2026 and Amazon shares from mid-2025. Ackman's rationale is based on his view that the market is overreacting to concerns about AI capital expenditure as a margin threat, while both companies demonstrate strong cloud growth, with Azure up 40% and AWS experiencing its fastest acceleration in 15 quarters.