U.S. stocks were mixed at Monday's open, with the Dow Jones Industrial Average and S&P 500 falling, while the tech-heavy Nasdaq Composite fluctuated. The technology sector was one of the few gainers, primarily due to a significant revenue boost for semiconductor stocks from AI startup Anthropic. However, the tech rally did not appear solid, with five out of the Magnificent Seven tech giants declining. Other sectors generally fell, with consumer discretionary, communication services, and basic materials performing the worst.