One of the joys of writing about business is that rare moment when you realise conventions are shifting in front of you. It brings a shiver down the spine. Vaingloriously, you start scribbling down every detail of your surroundings, as if you are drafting the opening lines of a bestseller. It happened to your columnist recently in San Francisco, sitting in the pristine offices of Anthropic, a darling of the artificial-intelligence (AI) scene. When Jack Clark, one of Anthropic’s co-founders, drew an analogy between the Baruch Plan, a (failed) effort in 1946 to put the world’s atomic weapons under UN control, and the need for global co-ordination to prevent the proliferation of harmful AI, there was that old familiar tingle. When entrepreneurs compare their creations, even tangentially, to nuclear bombs, it feels like a turning point.