Claude Fable 5.1 system prompt hardens song-lyric and copyright refusals

On 2 Sep 2026 Simon Willison documented major changes in Anthropic’s published Claude.ai/mobile system prompt for Fable 5.1 versus Fable 5. New rules forbid reproducing song lyrics, poems, or book/article passages in whole or in part (with pre-1929 works excepted when the date is known), and similarly block drawing copyrighted characters, logos, or covers even via SVG/code. The prompt also pushes briefer answers, drops “genuinely/honestly/straightforward,” softens end_conversation guidance in the published core prompt, adds harm-reduction redirects (dancesafe.org, tripsit.me, psychonautwiki.org), and states a reliable knowledge cutoff of end of June 2026. Anthropic publishes historic prompts on platform.claude.com; Willison notes the timing coincides with music-publisher litigation coverage.