S&P 500 today: Why the S&P 500 reversed today’s gains as the U.S. stock market opens 2026 on uneven footing - Dow Jones holds up while Nasdaq remains under pressure

S&P 500 Today: The S&P 500 Index opened higher on the first trading day of 2026 but soon dipped below the flat line, trading at 6,838.24 (down 0.11%). This reversal stems from a fading "Santa Claus rally" and investor caution over high valuations. The Dow traded near 48,120, up about 0.1%. The Nasdaq slipped more than 0.2%.