S&P 500 is now a 10-stock show. The top 10 companies control 42% of the index’s total value, smashing the Dot-Com record of 29%. Nvidia, Apple, and Microsoft alone make up nearly a quarter of the market, turning America’s biggest index into a tech-driven giant. The $19 trillion dominance of these firms means even one bad earnings miss could shake Wall Street. The S&P 500’s diversity is fading fast — and history shows peaks like this rarely end quietly.