Nvidia shares ended the day 17% lower, notching their worst one-day performance since March 2020 and closing solidly below the 200-day moving average. The decline erased $589 billion in market value, a record drop.

In a matter of days, DeepSeek proved to be so popular as to climb to the top of Apple's App Store, surpassing OpenAI's ChatGPT as the most downloaded app. But for owners of Nvidia stock, and stock traders in general, DeepSeek is on track of becoming a black swan — an unexpected event with extreme consequences.