Tool tutorial · XiaoHu Explains
Anthropic cut 80% of Claude Code's system prompt and replaced it with six new context rules
Rules became judgment, examples became interfaces — one tool description shrank from about 9,100 characters to a single sentence and an enum
⚑ This material comes from Anthropic's Thariq walking through the redesign of his own team's product. "Cut more than 80%" and "no measurable loss on coding benchmarks" are Anthropic's own figures — the original post doesn't say whether that's measured in characters or tokens, and doesn't list which benchmarks. The image showing conflicting instructions is labeled by Anthropic itself as an illustrative example, not an actual excerpt from a real prompt.
1 A counterintuitive number
They cut 80% of Claude Code's system prompt
Thariq Shihipar (@trq212), a member of Anthropic's technical staff, posted a long thread on X about something they'd just done to Claude Code: for the new Opus 5 and Fable 5 generation of models, they cut more than 80% out of the system prompt. Coding benchmarks showed no measurable loss.
Primary source and reference
- Thariq / Anthropic Original publisher