Anthropic adds text watermarking to older Claude models
What happened
Anthropic has again emailed API customers to announce that from 16 November 2026 it will add text watermarking to Claude Opus 4.6, Claude Opus 4.5, Claude Sonnet 4.5 and Claude Haiku 4.5. Reports note that the watermark can be bypassed under default sampling settings. The current state of play: Anthropic has notified customers and set out the effective date and the models covered.
Written by AI from the reports · updated 3 h ago
Timeline
Follow the reports to see the event from each side.
- The DecoderAnthropic's text watermark is easy to bypass on several older Claude models
Anthropic is rolling out text watermarks to four more Claude models ahead of the EU AI Act's December deadline. But on older models like Claude Opus 4.6 and Sonnet 4.6, API users can disable the watermark by changing a single sampling parameter. Anthropic's response to the loophole? A compliance warning.
Heat of this event
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