OpenAI has begun deploying textGrain, an invisible statistical signal designed to help approved investigators assess whether text may have been generated by certain OpenAI models. The company made the signal available as an opt-in for selected API models on 5 October and said it would roll it out to selected ChatGPT and Codex outputs in the European Union over the coming weeks.
The release is explicitly limited. OpenAI says access to its detector will be restricted to vetted researchers and other approved experts. It also warns that the signal does not establish authorship, ownership, accuracy or the identity of the person who produced a document. The absence of a detectable signal does not prove that text was written by a human.
OpenAI reports a target false-positive rate of 1 per cent and detection of about 80 per cent for 200-token passages, rising to about 95 per cent at 400 tokens in one psychology-oriented evaluation. The company also says editing weakens detection: replacing 25 per cent of the words in a 400-token passage reduced detection in its test from 92 per cent to 17 per cent.
For regulated organisations, the practical lesson is that watermarking can support investigations but cannot carry a disciplinary, compliance or fraud decision on its own. It should sit alongside access logs, document history, identity evidence and human review.
