New context engineering rules for Claude 5 generation models: Claude Code system prompt trimmed by over 80%

Claude 5 代模型上下文工程新规则：Claude Code 系统提示词精简超 80%

Anthropic published a blog post on how prompt engineering changes for Claude 5 generation models (Mythos, Fable, etc.). The key finding: new models no longer need verbose system prompts. Claude Code's system prompt was cut from 3,500 words to 600—over 80% reduction—with better performance. Three new rules: write instructions like documentation, use Markdown structure, and place constraints next to the content they constrain. The post doesn't disclose specific benchmark data or comparison baselines, so take the performance claim with a grain of salt.

Why it matters: Official Anthropic blog post with a real product experiment on Claude Code, delivering new prompt engineering rules for Claude 5-gen models. Concrete numbers (3,500→600 words, >80% reduction), three actionable rules, and a counterintuitive result that spreads naturally. Deduct...