The S&P 500 rose 1.49% to 7,764.70 on Sept. 21, nearing its August record even as market breadth deteriorated. Thirty components touched 52-week lows during intraday trading, compared with only seven reaching new highs. CNBC described the combination of a more than 1% index gain and more new lows than highs as the first such occurrence since late 1999, with July 23, 1929, the only earlier instance. The Nasdaq Composite gained 2.26% to a record, led by artificial-intelligence and semiconductor stocks, while AMD rose 9.95% and surpassed a $1 trillion market capitalization. Moderna and Warner Bros. Discovery also reached new highs on company-specific catalysts. MarketWatch said 60% of S&P 500 components were at least 20% below their all-time highs, compared with earlier data showing 59.2%. Analysts attributed the concentration to AI investment and megacap technology leadership, while tariffs, inflation, energy costs, elevated interest rates and expensive borrowing weighed on traditional sectors. Other strategists cautioned that economic and corporate earnings data had remained more resilient than expected during the first half of the year.