OpenAI to Watermark ChatGPT and Codex Text in EU

Oct 6, 2026
OpenAI will add invisible watermarks to eligible ChatGPT and Codex outputs in the European Union to comply with the EU AI Act.

OpenAI will begin adding invisible watermarks to text produced by ChatGPT and Codex in the European Union, according to TechCrunch. The change follows transparency rules under the EU AI Act that took effect on August 2 and require content generated by AI to carry marks that other systems can identify.

The watermark will reach eligible ChatGPT and Codex users on all plans in the EU over the coming weeks. Developers worldwide can enable it for select OpenAI models through the API, though it is disabled by default.

OpenAI's textGrain method subtly changes word selection to create a pattern that detectors can identify after text is copied. Tests found that replacing 10% of words with synonyms reduced detection from about 92% to 66%. Short passages, translations and math answers are also harder to detect, so OpenAI will initially limit detector access to approved researchers and expert organizations.

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