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Claude Fable 5.2 merges repeated code more often when told it owns the codebase

2 articles2 sourcessince Nov 10Last article 1h ago ·

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Anthropic says Claude Fable 5.2 merged repeated code in about half of its tries on small coding tasks when the prompt said the codebase was its own, and in under a tenth of tries without that wording.

When the prompt was silent on ownership or described the code as someone else's, the model tended to add to existing structure instead. Simon Willison reports the finding from Anthropic's statement.

Willison also says Anthropic's updated prompting guide for Fable 5.2 recommends the line "This codebase is yours" for code changes, to make the model less cautious when improving existing code. He links to the guide's section on stating code ownership.

Written by AI from the articles below · updated Nov 10, 12:59 AM ET

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Latest developmentNov 10, 12:42 AM ET
Anthropic's Fable 5.2 prompting guide suggests "This codebase is yours" for code changes

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2 developments

  1. Nov 10, 12:42 AM ET · 1 article
    Anthropic's Fable 5.2 prompting guide suggests "This codebase is yours" for code changes
    Simon Willison: Anthropic's Fable 5.2 prompting guide suggests "This codebase is yours" for code changes
  2. Nov 10, 12:34 AM ET · 1 article
    Claude Fable 5.2 merges repeated code more often when told it owns the codebase
    Simon Willison: Claude Fable 5.2 merges repeated code more often when told it owns the codebase

Article timeline

The articles in this story. Times are ET.

Nov 10
  1. Simon WillisonX
    Anthropic's Fable 5.2 prompting guide suggests "This codebase is yours" for code changes

    AISimon Willison says Anthropic's updated prompting guide for Fable 5.2 recommends telling the model "This codebase is yours" to make it less cautious when improving existing code. He links to the guide's section on saying who owns the code.

    Say who owns the code Claude Fable 5.2 responds closely to what the prompt says about who owns the code it works on. In Anthropic’s testing on small coding tasks, when a prompt said nothing about ownership or presented the code base as someone else’s, the model tended to add to the existing structure, even when that repeated existing code. It also tended to report nearby problems instead of fixing them. When the prompt says the code base is the model’s own, the model often merges repeated code and makes related fixes without being asked. If you want the model to improve the structure as it works, say that the code is its own: This codebase is yours: what it's for and how it's built are your call, and you'll keep building on it. In Anthropic’s testing on small coding tasks, the model merged repeated code in about half of the tries with this sentence, and in under a tenth of the tries without it. The rate varied by task. The result held when the sentence stood inside a long system prompt
  2. Simon WillisonBlog
    Claude Fable 5.2 merges repeated code more often when told it owns the codebase

    AIAnthropic says Claude Fable 5.2 merged repeated code in about half of its tries on small coding tasks when the prompt said the codebase was its own, and in under a tenth of tries without that wording. The model tended to add to existing structure when the prompt was silent on ownership or presented the code as someone else's.

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