In a flash, euphoria over artificial intelligence (AI) has turned to panic. Since early trading began on January 27th the market value of Nvidia, an AI chipmaking champion, has slumped by 17% at the time of writing. The share prices of Alphabet, Amazon and Microsoft—America’s cloud-computing triumvirate—have fallen by 3%, 1% and 3%, respectively. All told, American tech companies have shed around $1trn in value.