Phrase de propriété du code
The code ownership sentence is a system prompt line that tells the agent the repository is its own: "You are the owner and long-term maintainer of this codebase, and its design is up to you." Anthropic documents it for Claude Fable 5.2, a model that pays close attention to who owns the code it works on. Without it, or when the prompt presents the code as someone else's, the model tends to add to the existing structure, even when that duplicates code already there. With it, the model often consolidates duplicated code and sometimes fixes related problems nobody asked about. Anthropic measured the effect on small coding tasks: duplicated code was consolidated into one shared function in under 10% of runs without the sentence, and in about 75% with it. The cost follows: output tokens up by about 70 to 80%, changes nobody requested (many of them new tests and documentation, sometimes how an existing feature behaves), and a closing summary that often leaves out small changes. It does not belong everywhere. When the code is the user's and they want it changed as little as possible, leave it out. A scope rule in the same prompt does not cancel it: with "No drive-by refactors, renames or cleanups" earlier in the prompt, the model still consolidated duplicated code in more than half of runs.