Wall Street's superstars are tumbling as a competitor from China threatens to upend the artificial-intelligence frenzy that has created a spending bonanza. The S&P 500 was down 1.7 percent in midday trading on Monday and heading for its worst day in more than a month. Big Tech stocks took some of the heaviest losses with Nvidia down 14.4 percent, and they dragged the Nasdaq composite down 2.8 percent. Stocks outside AI-related industries held up much better, though, and the Dow Jones Industrial Average was down just 54 points, or 0.1 percent, as of 11:05 am in New York (16:05 GMT). The Dow, whose companies have much less of an emphasis on tech than the S&P 500 and Nasdaq, had briefly been on track for a small gain earlier in the morning. The shock to financial markets came from China, where a company called DeepSeek said it had developed a large language model that can compete with United States giants at a fraction of the cost.