Claude Fable 5’s Full System Prompt Just Got Leaked

Source: YouTube Short — Nick Automates (:32)

Claim

Someone leaked Claude Fable 5’s full system prompt right after release:

• ~120,000 characters, 1,500+ lines
• Covers the exact instructions Anthropic uses to control how the model “thinks, plans, and gets things done”
• The pitch: inject these same instructions into cheaper open-source models (GLM 5.2 / Kimi K2.7) so they follow Anthropic’s playbook — claimed to significantly improve results

Creator gated the actual link behind a comment keyword (“Fable”), so the leak URL isn’t captured here.