I had been sleeping on Claude's ability to write books until a couple of days ago I had it write a novel set in the Accelerando universe. It whipped up a very convincing complete multi-Act 13 chapter side plot about humans learning to interact with Economics 2.0. It was quite good though I'm sure cstross would be horrified.
Yesterday, I had Claude 3.7 write a full 80,000-word novel. My prompt was a bit longer, but the result was shockingly good. The new thinking mode is very impressive.