Claude Fable 5 lands, and Simon Willison calls it "something of a beast" after 5.5 hours.

Anthropic shipped Fable 5 on June 9. Willison spent ~5.5 hours stress-testing it: slow and expensive, but it handled everything he threw at it, including agentic coding. (Simon Willison) The tell that it's a real working model and not a benchmark queen: because it post-dated AgentsView's pricing database, he used Fable to reverse-engineer the tool and derive a custom-pricing recipe. That's the kind of use that doesn't show up on a leaderboard but tells you the model is actually useful for hard, open-ended work.