Anthropic Context Engineering Guide: System Prompts Under 2,000 Tokens, Static/Dynamic Split for Prefix Caching, Context Rot Above 40% Window
Anthropic Engineering·medium signal
Anthropic's engineering blog publishes production guidance: keep system prompts under 2,000 tokens (most teams overload with 10%-relevant info); split static context (identity, schemas, rules at front for prefix caching) from dynamic context (current input, tool outputs in variable suffix); context rot degrades recall accuracy before hitting the hard limit. Curate minimal tool sets — bloated tool libraries cause ambiguous routing failures.