Berkshire and Ackman Build Mega-Cap Tech Stakes: MSFT New Position, AMZN Doubled

First-quarter 13F filings have revealed that two of the market's most influential investors, Warren Buffett and Bill Ackman, are aggressively buying mega-cap technology stocks, a signal that could reinforce the concentration narrative and extend the AI rally. Berkshire Hathaway's Greg Abel, in his first quarter as CEO, increased Berkshire's Alphabet position and added a new 5.65 million share stake in Microsoft at an average cost of approximately 21 times forward earnings. Simultaneously, Berkshire nearly doubled its Amazon stake by 1.84 million shares, signaling confidence in the e-commerce giant's AWS division and AI infrastructure play.

Bill Ackman's Pershing Square Capital Management similarly established a meaningful position in Microsoft, with Ackman's commentary suggesting he views the stock as having structural advantages in the AI era due to its enterprise relationships, Azure cloud platform, and integration with OpenAI. The timing is notable: Ackman entered at valuations that other value investors have called excessive, yet his rationale mirrors Buffett's historical playbook of buying quality businesses at premium multiples if the quality itself justifies the multiple. Ackman specifically noted Microsoft's flexibility to maintain competitiveness and its ability to defend market share against new entrants.

These moves are emblematic of a shift in the investment management industry: even traditionally skeptical value investors like Ackman are ceding ground to the idea that mega-cap tech dominance in the AI era is justified and defensible. The insider buying also reduces risk aversion among other institutions: if Buffett and Ackman are buying, the downside is implicitly being bid for by highly capitalized, sophisticated investors. This creates a feedback loop where mega-cap tech becomes increasingly attractive on the belief that the smartest money thinks it's cheap or at fair value.

However, the risks remain: if the market rotates away from mega-cap concentration, these positions could face meaningful drawdowns. Additionally, if Microsoft and Amazon disappoint on AI capex returns or if competition accelerates, the premium valuations could contract sharply. The filing of positions also creates potential agency issues for retail investors following mega-cap allocations blindly without understanding the fundamental shifts required to justify current valuations.