New context engineering rules for Claude 5 generation models

The new rules of context engineering for Claude 5 generation models

Anthropic describes its context engineering approach for the Claude 5 generation models, cutting the Claude Code system prompt for Claude Opus 5 and Claude Fable 5 by more than 80% with no measurable loss on coding evals.

Why it matters: Anthropic splits context management into lightweight repo notes, on-demand skills and specific reference files, a transferable way to cut repeated instructions and over-constraint.