Claude Fable 5.1 watermark: It has a blind spot developers can’t ignore

Anthropic released Claude Fable 5.1 with a watermarking system that embeds a statistical signature in generated text to indicate AI involvement. This watermark alters token randomness without affecting output quality but is limited in code generation to avoid accuracy issues. The watermark is part of the text itself and cannot be removed by copying, and Anthropic plans to apply it globally and to older models.