According to @StockMarketNerd, the S&P 500 is roughly 4% below its all-time high and recent gains are concentrated in a small cohort of mega-cap leaders often referred to as the S&P 10, highlighting narrow market breadth. Source: @StockMarketNerd on X, Nov 20, 2025. Concentrated leadership and narrow breadth historically increase index fragility by raising drawdown risk and reducing diversification benefits, which can affect short-term momentum and volatility. Source: S&P Dow Jones Indices research on market concentration and breadth. For crypto, risk-on phases in U.S. equities near highs with tech-led leadership have coincided with stronger BTC and ETH beta via positive cross-asset correlations, making breadth and mega-cap performance useful signals for crypto exposure. Source: Coin Metrics research on BTC–equity correlations.