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

Anthropic's September 1 system prompt for Claude Fable 5.1, the instructions behind its consumer apps, tells the assistant not to reproduce song lyrics, poems or passages from books and articles. Once it has declined such a request, it keeps declining narrower or reworded versions for the rest of that conversation and offers to describe or analyze the work instead. Works first published before 1929 are allowed, but the assistant goes by what it knows of the work's date rather than the user's say-so, and declines when unsure. Published system prompt.

Simon Willison compared the new prompt with the one for the previous model, Fable 5, and called this lyrics section the most interesting difference between them. The published text shows the intended behavior; it does not measure how consistently the model follows it, and Willison notes that some feature-specific instructions are not part of the published core prompt. Prompt comparison.