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  2. Simon Willison — Creator of Datasette; co-creator of Django/

Claude's new system prompt really doesn't want to reproduce song lyrics

Blog · Watch/Read · (gathered 2026-09-03)

  • Simon Willison highlights significant changes in Anthropic’s Claude Fable 5.1 system prompt, revealing the company’s evolving policies on content generation and user interaction, often in response to legal and ethical pressures.
  • Fable 5.1 now explicitly forbids reproducing song lyrics (likely due to recent lawsuits) and copyrighted visual works/characters, offering creative alternatives like a “skateboarding axolotl” instead of Sonic.
  • Willison discovered that crucial operational guidelines, such as those for the end_conversation tool, exist in “different layers” beyond the publicly published core prompt, indicating not all system instructions are transparently shared.
  • New guidelines for illegal substances now direct users to specific harm-reduction websites (e.g., dancesafe.org), marking the first time Claude’s system prompt includes external URLs not hosted by Anthropic.