Claude Fable 5.2 prompt guide: reducing early stopping and unnecessary approval requests(platform.claude.com)

- Anthropic's official documentation lays out how to write instructions suited to Claude Fable 5.2. It says the effort level, a setting that determines how much the model thinks, should start at the default of high and be raised or lowered based on your own evaluation. It advises re-comparing values tuned for earlier models rather than reusing them as they are. - In long tasks, the model sometimes stops with work left over, and this happens more often at low and medium. When Anthropic re-ran recorded sessions at medium, adding a phrase telling the model to finish the job cut sessions that ended with work remaining by about half, and output tokens increased by about 30%. - When the prompt stated that the code was the model's own, the rate of merging duplicate code rose to about half of attempts, and without that statement it was below 1 in 10. This is the result of a small coding test by Anthropic, and in it output tokens rose by about 1.5 times and unrequested changes also appeared. - Approval rules are applied exactly as written, so the target actions must be specified precisely. In an Anthropic simulated test, when sending messages to outside parties was listed as requiring approval, the model did not carry out about half of routine requests to send messages to colleagues or other teams.