AI earnings drive US stocks as concentration hits 95th percentile
Expectations of rising corporate profits from artificial intelligence are driving US equity valuations and insulating markets from shocks, an ECB analysis finds. However, market concentration in the S&P 500 has climbed above its historical 95th percentile.
Profit expectations fuel equity gains
US equity valuations have expanded since November 2022, primarily driven by rising corporate profitability expectations linked to the artificial intelligence boom.
A dividend discount model decomposition shows that higher earnings expectations—rather than lower discount rates or falling risk premia alone—serve as the primary driver of US risk asset prices.
Concurrently, the distribution of equity risk premia across S&P 500 firms has compressed, falling close to zero at the 25th percentile, with pronounced tightening across technology and industrials.
This heightened risk appetite has insulated US equities from macro and geopolitical shocks, including the Middle East conflict in March 2026.
Concentration exceeds historical norms
Market concentration creates growing vulnerabilities despite favourable risk pricing.
The Herfindahl-Hirschman Index has risen above the 95th percentile for the S&P 500 and above the 75th percentile for information technology.
While the median risk price in tech remains compressed, the distribution tails have widened as investors demand higher compensation for higher-risk stocks.
Underperformance by a few mega-cap firms could trigger broad declines and challenge debt-funded AI investments.
A narrow foundation for optimism
The analysis pinpoints the fragility beneath buoyant headline valuations.
Relying on projected earnings to suppress risk premia ignores the danger of extreme index concentration.
Any stumble among mega-cap tech leaders will quickly test the resilience of the broader financial system.
Source: US equity market developments during the AI boom
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