Simon Willison · 2026-09-02 · notable
Simon Willison — Claude's new system prompt refuses to write song lyrics
Simon Willison read Anthropic's published Claude Fable 5.1 system prompt and found a new copyright section: Claude will not reproduce song lyrics, poems or book passages, and will not draw known characters, logos or album covers in code.
Anthropic published the Claude Fable 5.1 system prompt, and its longest new section is about not reproducing other people's work.
What is it?
Willison's post walks through the Claude Fable 5.1 system prompt Anthropic published on September 1 and pulls out what changed since Claude Fable 5. The largest addition is a copyright block: Claude declines to reproduce song lyrics, poems, or passages from books and articles, in whole or in part, and keeps declining reworded versions for the rest of the conversation. Works first published before 1929 are still allowed.
How does it work?
The same rule is extended to anything Claude draws with code — SVG, canvas, CSS, HTML mockups, plotting scripts, ASCII art. The prompt tells Claude to judge a request by what the finished picture would add up to rather than by what it names, so describing a character instead of naming it does not get around the rule. Willison also flags smaller edits: shorter replies, dropping the words "genuinely" and "honestly", harm-reduction pointers to dancesafe.org and tripsit.me for drug questions, and the removal of the end_conversation tool.
Why does it matter?
System prompts are where a lab's legal position becomes a behavior developers hit in production. Willison points out that Sony Music Publishing and Warner Chappell sued Anthropic over lyrics days before this section appeared, which makes the timing hard to miss. For anyone building on Claude, the practical read is that a whole class of prompts — quote this song, draw this logo, recreate this cover — now fails on claude.ai and the mobile apps by design, though Anthropic notes these prompt updates do not apply to the API.
Who is it for?
developers building on Claude and people tracking AI copyright