Anthropic deleted 80% of Claude Code's system prompt — and says stop giving Claude 5 models examples

Claude by Anthropic·high signal

Anthropic removed "over 80% of Claude Code's system prompt" for Opus 5 and Fable 5 with "no measurable loss on our coding evaluations," publishing the new rules the same day Opus 5 shipped. The most counterintuitive rule is to stop few-shotting: "with our newest models, we've found that giving examples actually constrains them to a certain exploration space" — design expressive tool interfaces instead. The CLAUDE.md guidance is equally concrete: "keep your CLAUDE.md lightweight and briefly describe what your repo is for, but spend most of the tokens on gotchas inside of the codebase," and replace hard rules with judgment-enabling phrasing (their example: swap "Never write multi-paragraph docstrings — one short line max" for "Write code that reads like the surrounding code: match its comment density, naming, and idiom").