Claude Code System Prompt Reduced by Over 80% for Opus 5 and Fable 5

A significant change was made to Claude Code. The system prompt was heavily modified. Over 80% of the prompt was removed. This change applies to Opus 5. It also applies to Fable 5. The reduction aims to optimize the system. This affects how the code interacts with prompts. Developers are noting the scale of the removal. It represents a major shift in prompt structure. The implications for performance are being observed.