IT IS Common lore in Silicon Valley that no company has a bigger moat than Nvidia, the world’s dominant supplier of chips for artificial intelligence (AI). That was true until January 27th, when a Chinese firm called DeepSeek, bearing an AI model that it said cost less than $6m to train, blew a nearly $600bn hole in the value of the semiconductor giant, marking the biggest one-day loss in the history of America’s stockmarket. Think of it as the 21st-century equivalent of a shot from a trebuchet, the medieval contraption capable of reducing castle walls to rubble. Have Nvidia’s defences finally been breached?