OpenAI is rolling out textGrain watermarking to eligible ChatGPT and Codex users in the European Union over the coming weeks. API customers worldwide can opt in starting October 5; watermarking remains off by default globally.
OpenAI says textGrain matched or exceeded other approaches like Google DeepMind’s SynthID for text. Anthropic announced similar watermarking in August for EU AI Act compliance but applied it worldwide.
OpenAI notes textGrain does not guarantee reliable detection. Editing 10% of words with synonyms dropped detection from ~92% to 66%. Short passages, math answers, and translated text are harder to detect.
Detector access will initially be limited to approved researchers and expert organizations. The watermark indicates OpenAI-generated content but cannot identify users, verify accuracy, or prove human authorship.