Top 10 U.S. stocks now account for 40% of the S&P 500, with $303 billion spent on AI data centers in early 2026 alone.
The S&P 500 and Nasdaq have climbed 82% and 100% over the past three years, fueled by surging AI stocks. Mega-cap tech companies now dominate the index, with the top 10 holdings representing 40% of its weight, raising concentration risks.
Amazon, Alphabet, Microsoft, and Meta spent a combined $303 billion on data centers in the first half of 2026, tripling their investment over five years. While these firms argue AI demand will justify the spending, valuation metrics like the Shiller CAPE Ratio suggest potential overvaluation.
The market’s reliance on a handful of AI-driven stocks draws comparisons to the dot-com bubble, though it remains unclear whether a correction is imminent.