US stocks dropped sharply Monday — and chipmaker Nvidia lost nearly $600 billion in market value — after a surprise advancement from a Chinese artificial intelligence company, DeepSeek, threatened the aura of invincibility surrounding America’s technology industry.

Entrepreneur Marc Andreessen, known for co-writing Mosaic, one of the world’s first web browsers, wrote Sunday on X that “DeepSeek R1 is AI’s Sputnik moment,” likening it to the space race between the U.S. and the Soviet Union and the event that forced the U.S. to realize that its technological abilities were not unassailable.

Here’s what you need to know about DeepSeek, the Chinese AI startup that rattled markets as its app dethroned OpenAI's as the most-downloaded free app in the U.S. on Apple.