OpenAI is rolling out an invisible text watermarking technology called textGrain to eligible ChatGPT and Codex users across all plans in the European Union over the coming weeks from October 5, 2026

From the articleOpenAI is adding text watermarking in ChatGPT and CodexAlso in OpenAI will watermark ChatGPT text in the EU but makes it optional for API users worldwide, OpenAI will start watermarking ChatGPT’s text in the EU