The new rules of context engineering for Claude 5 generation models are six then/now shifts moving agent 📝Context Engineering away from prescriptive scaffolding and toward judgment, interface design, and context loaded on demand.
The rules were published July 24, 2026 by Thariq Shihipar, a member of technical staff at 📝Anthropic, and rest on a single operational datum: the team removed more than eighty percent of 📝Claude Code's system prompt for advanced Claude 5 models and measured no performance loss. That figure is Anthropic's own report on its own product and has not been independently replicated.
Each rule is framed as a then/now pair. Rules give way to judgment — instead of enumerating prohibitions, a prompt states the standard and lets the model apply it. Examples give way to interface design, on the reasoning that worked examples constrain exploration in stronger models while expressive tool parameters and clear enumerations hint at correct use without narrowing it. Front-loaded context gives way to progressive disclosure, pulling material in through skills and deferred loading rather than shipping all of it in the system prompt. Repetition across the system prompt and tool definitions gives way to one clear tool description. Hand-maintained 📝CLAUDE.md memory gives way to 📝Claude Code Memory's automatic capture. And simple markdown specs give way to rich references — code examples, test suites, HTML artifacts, and rubrics the model can verify its own work against.
The through-line is that each shift removes instruction the model no longer needs and replaces it with structure the model can navigate. That makes the six a version boundary rather than a style preference: a prompt tuned for an earlier generation is not merely verbose on a Claude 5 model, it actively constrains one. Practitioners carrying large system prompts, example libraries, or hand-curated memory files forward from earlier models have inherited scaffolding worth auditing rather than porting.
Rules three and five describe the architecture I already run — my global instruction file is a pointer that names where context lives instead of carrying it, and the library loads on demand through MCP. What this article actually asks for is a subtraction pass: find the scaffolding that outlived the model it was written for.