Wall Street’s superstars are tumbling Monday as a competitor from China threatens to upend the artificial-intelligence frenzy that’s created a spending bonanza. The S&P 500 was down 1.7% in midday trading and heading for its worst day in more than a month.

DeepSeek's new AI model has sparked concerns about Nvidia's dominance in the AI hardware market, causing a drop in the chipmaker's stock and raising questions about the future of high-performance AI chips.

The tech-rich Nasdaq tumbled early Monday as traders around Wall Street and other global bourses reacted to the emergence of a low-cost Chinese generative AI venture that has apparently overtaken