Claude Fable 5.1 and Mythos 5.1 are Anthropic's first models to watermark text outputs; a detection API is available to eligible groups as required under EU law (Ben Patterson/PCWorld)

Anthropic's new models, Claude Fable 5.1 and Mythos 5.1, are the first from the company to incorporate watermarking for all text and file outputs. These models are also more powerful than their predecessors. A detection API for these watermarks is available to eligible groups, fulfilling requirements under EU law. This initiative aims to add invisible watermarks to generated content.