Key Takeaways
- • S&P 500 Momentum Index surged 32% over a two-month period, driven almost entirely by AI-related stocks that now represent 45% of the index's market capitalization, according to recent data cited across multiple sources.
- • The S&P 500 ex-AI Index has remained essentially flat since February, gaining only 5.07% year-to-date, while the headline index climbed 76% over three years—demonstrating that AI stocks alone account for the vast majority of market gains and raising concerns about concentration risk.
- • The benchmark S&P 500 closed above 7,500 for the first time, having surged more than 18% since March 30, 2026, with semiconductor and hyperscaler stocks including Snowflake (up 37%), Micron, and others leading the rally on AI-driven demand.
- • First-quarter S&P 500 earnings are tracking to climb nearly 29% year-over-year, with most growth attributable to AI-related heavyweights, suggesting fundamental support for valuations in the technology sector.
- • The concentration of gains in a handful of AI giants has raised institutional concerns about market breadth and the sustainability of the current bull market, as traditional diversification benefits have eroded significantly.
Summary
The S&P 500 achieved record highs in late May 2026, driven by an unprecedented surge in artificial intelligence-related equities. The momentum index gained 32% over a two-month period, breaking through the 7,500 level for the first time as investors rotated aggressively into AI stocks. The S&P 500 climbed 17% over eight weeks, marking its 20th largest rally streak in history. However, this headline performance masks a deeply bifurcated market dynamic that institutional investors must carefully consider.
Strip away AI-related stocks, and the broader market narrative collapses. The S&P 500 ex-AI Index, which excludes artificial intelligence enablers, has gained only 5.07% since its February 2026 launch and fell 1.84% from inception, according to Google Finance data. Over a three-year period through early 2026, Goldman Sachs analysis cited in multiple reports shows the headline S&P 500 returned 76% versus just 32% for the non-AI version—a stark divergence that underscores the concentration risk embedded in current valuations. AI-linked stocks now account for a record 45% of the S&P 500's market capitalization, meaning approximately half the index is dependent on a single thematic sector.
The rally accelerated sharply following March volatility, with the index gaining 15.5% since March 30 alone, driven by strong earnings expectations and investor enthusiasm for hyperscaler companies. First-quarter S&P 500 earnings are tracking to climb nearly 29% year-over-year, with Wall Street's AI-related heavyweights contributing disproportionately to this growth. Semiconductor stocks led gains, with individual names like Snowflake surging 37% and Micron reaching $1 trillion in market value. Reports of strategic deals—including Intel's arrangement to manufacture chips for Apple—further catalyzed sector-wide momentum.
The market's reliance on AI-driven gains has created what institutional observers describe as a concentration risk. While earnings growth provides fundamental support for technology valuations, the uneven distribution of market returns raises questions about the sustainability of the current bull market and the breadth of the underlying rally. For hedge funds and alternative investment managers, the divergence between headline index performance and the ex-AI index performance represents a critical consideration for portfolio construction and risk management.
Strip away AI-related stocks, and the broader market narrative collapses. The S&P 500 ex-AI Index, which excludes artificial intelligence enablers, has gained only 5.07% since its February 2026 launch and fell 1.84% from inception, according to Google Finance data. Over a three-year period through early 2026, Goldman Sachs analysis cited in multiple reports shows the headline S&P 500 returned 76% versus just 32% for the non-AI version—a stark divergence that underscores the concentration risk embedded in current valuations. AI-linked stocks now account for a record 45% of the S&P 500's market capitalization, meaning approximately half the index is dependent on a single thematic sector.
The rally accelerated sharply following March volatility, with the index gaining 15.5% since March 30 alone, driven by strong earnings expectations and investor enthusiasm for hyperscaler companies. First-quarter S&P 500 earnings are tracking to climb nearly 29% year-over-year, with Wall Street's AI-related heavyweights contributing disproportionately to this growth. Semiconductor stocks led gains, with individual names like Snowflake surging 37% and Micron reaching $1 trillion in market value. Reports of strategic deals—including Intel's arrangement to manufacture chips for Apple—further catalyzed sector-wide momentum.
The market's reliance on AI-driven gains has created what institutional observers describe as a concentration risk. While earnings growth provides fundamental support for technology valuations, the uneven distribution of market returns raises questions about the sustainability of the current bull market and the breadth of the underlying rally. For hedge funds and alternative investment managers, the divergence between headline index performance and the ex-AI index performance represents a critical consideration for portfolio construction and risk management.
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