When Dario Amodei gets excited about AI—which is nearly always—he moves. The cofounder and CEO springs from a seat in a conference room and darts over to a whiteboard. He scrawls charts with swooping hockey-stick curves that show how machine intelligence is bending toward the infinite. His hand rises to his curly mop of hair, as if he’s caressing his neurons to forestall a system crash. You can almost feel his bones vibrate as he explains how his company, Anthropic, is unlike other AI model buil...