EW YORK (AP) — Wall Street’s superstars are tumbling Monday as a competitor from China threatens to upend the artificial-intelligence frenzy they’ve been feasting on.

The S&P 500 was down 1.8% in afternoon trading and heading for its worst day in more than a month. Big Tech stocks took some of the heaviest losses, with Nvidia down 17.4%, and they dragged the Nasdaq composite down 3.5%.

Stocks outside of AI-related industries held up much better, though, and the Dow Jones Industrial Average was up 160 points, or 0.4%, as of 2:02 p.m. Eastern time. The Dow has much less of an emphasis on tech than the S&P 500 and Nasdaq.

The shock to financial markets came from China, where a company called DeepSeek said it had…