The new rules of context engineering for Claude 5 models
Anthropic shares updated best practices for context engineering with Claude 5 models (Opus 5, Fable 5). Key finding: previous system prompts and constraints were over-restrictive; newer models have better judgment, allowing significant simplification. They removed 80% of Claude Code's system prompt with no measurable loss on coding evals. Article contrasts old practices (give rules, give examples, put everything upfront, repeat yourself, memory in CLAUDE.md, simple specs) with new ones (let model use judgment, design interfaces, progressive disclosure, simple tool descriptions, auto-memory, rich references). Recommendations: keep CLAUDE.md lightweight focusing on repo-specific gotchas; use Skills as on-demand lightweight guides; use progressive disclosure to avoid context bloat; prefer code references over descriptions. Includes introduction of `claude doctor` command for automatic simplification. For engineers using Claude Code or building Claude-based agents.