U.S. stock valuations have reached historic highs, with the market capitalization of U.S. stocks relative to the M2 money supply hitting 289%, the highest level since the 2000 Dot-Com Bubble. Over the past two years, this ratio has surged by approximately 100 percentage points. Additionally, the largest 10% of U.S. stocks now account for a record 75% of the market, surpassing the concentration seen before the Great Depression and exceeding the 73% share at the peak of the Dot-Com Bubble. Analysts indicate that the current premium in U.S. stocks is largely driven by technology, which has struggled to maintain momentum, resulting in U.S. stock returns ranking 14th among the 23 largest global markets this year. The high valuations and market concentration are causing concern among investors, as the largest stocks have not been this expensive since the dot-com era.