🚨 BREAKING: Someone just leaked the full system prompt of Claude Fable 5.
Anthropic launched it on June 9. The prompt was public on GitHub within 24 hours.
120,000 characters. 1,585 lines. 27,000 tokens. Every hidden instruction exposed.
It's sitting in the CL4R1T4S repo by Pliny the Liberator. 26.4K stars. The same repo that leaked ChatGPT, Gemini, Grok, Cursor, Lovable, Replit, and Perplexity prompts.
Here's what the Claude Fable 5 prompt actually reveals:
→ Fable 5 and Mythos 5 share the same underlying model. Fable gets extra safety measures. Mythos doesn't, but it's restricted to approved organizations only.
→ Knowledge cutoff is end of January 2026. Not May. Not March. January.
→ Claude is explicitly told to avoid bullet points, headers, and lists unless the user asks. That "why does Claude write in prose now" question everyone had? It's in the prompt.
→ Copyright hard limit: quoting 15 words from any single source is flagged as a "SEVERE VIOLATION." One quote per source maximum. After one quote, that source is closed.
→ New persistent storage API lets artifacts store and retrieve data across sessions using key-value pairs.
→ MCP app connectors are built into the prompt. Claude can search for and suggest third-party integrations mid-conversation.
→ The prompt includes detailed instructions for Claude Cowork, Claude in Chrome, Claude in Excel, and Claude in PowerPoint as tools Claude can use.
→ This prompt is specific to Claude. ai's consumer chat interface. API users get no system prompt. Claude Code has its own separate instructions.
The original X post hit 700K views in its first two days.
26.4K GitHub stars. 4.7K forks..