A company called DeepSeek said it had developed a large language model that can compete with U.S. AI giants but at a fraction of the cost. DeepSeek had already hit the top of the chart for free apps on Apple’s App Store by Monday morning, and analysts said such a feat would be particularly impressive given how the U.S. government has restricted Chinese access to top AI chips.

The Nasdaq Composite, which tracks the country's largest tech firms, plunged more than 3%. The Dow ended up nearly 300 points after falling earlier in the day, and the S&P 500 tumbled almost 1.5%.