Shares of Nvidia fell 9.5% today as the market frets about slowing progress in AI.

There were worries last week after earnings but shares of Nvidia steadied after nearly a dozen price target boosts from analysts. But that would only offer a temporary reprieve as a round of profit-taking hit today and snowballed.

The result was a decline of $278 billion, which is the worst ever market cap wipeout from a single stock in a day.