Claude Fable 5 Frontier Model Lands; Simon Willison Calls It 'Something of a Beast' After 5.5-Hour Test

Simon Willison·medium signal

Anthropic shipped Claude Fable 5 on June 9; Simon Willison spent ~5.5 hours stress-testing it and described it as slow and expensive but effectively handling everything he threw at it, including agentic coding work. Because it post-dated AgentsView's pricing database, he used Fable to reverse-engineer the tool and derive a custom-pricing recipe — a signal the model is being put to real agentic use, not just benchmarked.