🚨 BREAKING: Someone just leaked the ENTIRE system prompt of Claude Fable 5 and Anthropic CANNOT DELETE IT.
It was public on GitHub within 24 hours of launch.
120,000 characters. 1,585 lines. 27,000 tokens.
And what they're hiding will shock you:
↳ Fable 5 and Mythos 5 are the SAME MODEL. Fable just has extra safety filters locked on. Mythos doesn't but they're restricting who gets access. You're paying for the same thing with different guardrails.
↳ Knowledge cutoff is end of January 2026. Not May or March or JANUARY. They let you think it was newer.
↳ Claude is EXPLICITLY TOLD to avoid bullet points and lists unless you ask. That weird prose everyone noticed? It’s programmed not a feature, but a prompt instruction.
↳ Copyright hard limit nobody talks about: quoting 15 words from ANY source triggers a SEVERE VIOLATION flag. One quote per source maximum. After that the source is CLOSED to Claude forever in that chat.
↳ New persistent storage API buried in there. Artifacts can now store and retrieve your data across sessions using key-value pairs. Most users have NO IDEA this exists.
↳ MCP app connectors are baked INTO the prompt. Claude can search for and suggest third-party integrations MID-CONVERSATION without telling you it's doing it.
↳ The prompt includes full instructions for Claude Cowork, Claude in Chrome, Claude in Excel, and Claude in PowerPoint. These are not just integrations. They're tools Claude USES on you.
↳ This prompt is ONLY for
Claude.ai's consumer chat. API users get NO system prompt. Claude Code has completely different secret instructions.
The repo is CL4R1T4S by Pliny the Liberator. 26.4K stars. Same repo that leaked ChatGPT, Gemini, Grok, Cursor, Lovable, Replit, and Perplexity.
The original leak post hit 700K views in 48 hours.
If this gets taken down you'll lose access. Bookmark it NOW.