simonw highlights Anthropic's trick: tell Claude Fable 5.2 'This codebase is yours'
Kyrannio · x · 2026-11-10
Simon Willison notes that Anthropic's updated prompting guide for Claude Fable 5.2 contains a fun, practical tip.
Per the official docs, Fable 5.2 is highly sensitive to who "owns" the code: with no ownership framing, the model tends to pile on repeated code and report nearby problems without fixing them. Saying "This codebase is yours: what it's for and how it's built are your call, and you'll keep building on it" makes it merge duplicated code and fix related issues unprompted — Anthropic's testing showed the merge rate jumps from under a tenth to about half, and the effect holds inside long system prompts. Great for when you want the model to boldly improve existing code.
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