The concentration of market capitalization in the US stock market has reached levels not seen in the past 100 years, with the top 10 stocks in the S&P 500 accounting for over 35% to nearly 37% of the index's total market value. This concentration surpasses levels observed during the Great Depression and the IT bubble, indicating a significant erosion of risk diversification across the market. The largest stock's market capitalization is approximately 750 times greater than that of the 75th percentile stock, marking the widest disparity since the 1930s. Additionally, US equities remain richly valued compared to Chinese stocks, with the price-to-earnings premium gap near historic highs. The S&P 500's market capitalization relative to GDP stands at about 168%, considerably higher than the global equity markets average of around 90%, suggesting that US stocks are exceptionally expensive. These factors collectively raise concerns about potential market vulnerabilities and the risk of corrections driven by the underperformance of a few dominant stocks.