Simon Willison Details Hands-On Experience With Anthropic's Claude Fable 5

Simon Willison

Jun 13, 2026

Simon Willison characterizes Anthropic's new Claude Fable 5 as a slow, expensive, but highly capable model that he suspects is the largest yet from any vendor. He supports this verdict by noting the model upgraded his micropython-wasm library to full Python and added human-in-the-loop approval features within his Datasette Agent.

View the full update on simonwillison.net

Simon Willison

@simonw4d ago

Wrote up my initial impressions of Claude Fable 5 - it has a big model smell: slow, expensive and capable of crunching through pretty much everything I threw at it https://t.co/xLybVGiR4c

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