Billionaire hedge fund manager Bill Ackman disclosed this week that Pershing Square built a significant position in Microsoft during the first quarter of 2026, buying into the stock after it dropped following a January earnings report that spooked investors over the pace of Azure cloud revenue growth. Ackman called the entry point a "once in a decade" opportunity to buy the most important AI infrastructure company at 21 times forward earnings.

In his quarterly investor letter, Ackman laid out a thesis centered on two core convictions. First, that Azure is positioning itself as the default cloud infrastructure for enterprise AI workloads, benefiting from Microsoft's exclusive partnership with OpenAI and a multi-year lead in integrating AI across its product stack. Second, that Microsoft 365 Copilot, priced at $30 per user per month, represents the largest upsold revenue opportunity in enterprise software history, with hundreds of millions of existing Microsoft 365 users as the addressable market.

Ackman compared the Microsoft investment to previous Pershing Square purchases of Alphabet, Amazon, and Meta, all of which were acquired during periods of market skepticism around AI spending. Those positions generated strong returns as the market eventually priced in accelerating AI revenue. He is betting Microsoft follows the same pattern.

The Broader Smart Money Signal

Ackman is not alone. The same OGE financial disclosures released this week showed President Trump also bought between $1 million and $5 million in Microsoft stock in Q1. Techmeme's leaderboard shows Microsoft as the most accumulated AI stock among institutional investors in the latest 13F filing wave. Pershing Square also recently listed its new closed-end fund, Pershing Square USA, on the NYSE in late April, marketed toward retail investors who want exposure to Ackman's concentrated portfolio.

The timing is also worth noting. Ackman bought during a period when Copilot adoption data was mixed and Azure growth was being questioned. Since then, Microsoft reported accelerating Azure revenue in its April quarter, Copilot hit 5 million paying enterprise seats, and the company expanded its OpenAI partnership with a new revenue-sharing structure that kicked in when OpenAI's restructuring completed. The stock has recovered most of its post-January losses.

The Risk He Is Underweighting

The obvious counter-thesis: Microsoft is spending enormous sums on AI infrastructure with uncertain returns. Capital expenditure is projected above $80 billion for fiscal 2026. If enterprise AI adoption takes longer than expected to translate into recurring revenue, the company's margins will compress before Copilot and Azure growth can offset the spending. Ackman's letter acknowledged this risk but argued that Microsoft's distribution moat across 300 million commercial Office users makes it the highest-probability winner in enterprise AI, even if the timeline stretches.

Separately, Ackman disclosed that Pershing Square sold its Alphabet position during the same quarter. He said the sale was not a bet against Google but a capital reallocation toward what he views as a higher-conviction AI play. In Ackman's framing, the AI race has narrowed to an infrastructure question, and Microsoft owns the most infrastructure.

Sources: CNBC (May 15), Business Insider (Theron Mohamed, May 15), 247 Wall St. (May 15), Reuters (Mihika Sharma, May 16), Pershing Square Q1 2026 investor letter.