Anthropic Is Watermarking Four More Claude Models — With One Catch
Anthropic is expanding its invisible text watermark to four more Claude models on November 3, 2026 — Claude Mythos 5, Claude Opus 4.7, Claude Opus 4.6 and Claude Sonnet 4.6 — according to a customer email reported on November 1. The move extends a marking system already running on newer models like Claude Opus 5.5, and it is tied to the European Union's AI Act transparency deadline in December. What Is Changing on November 3 The four models join Anthropic's watermarking rollout in stages. The newer models already carry the mark; these four are older models released before August 2, 2026, which had a transition period under the EU rules. Rollout on the Claude Platform starts November 3, while Amazon Bedrock may follow a few days later, per the customer notice. How the Invisible Watermark Works Nothing visible changes. Anthropic's watermark does not add characters, a notice, or metadata you can see. Instead, it subtly changes the randomness behind the model's word choic...