What changed
OpenAI introduced textGrain, a statistical watermark embedded during generation. Select API customers can opt in globally now, while ChatGPT and Codex rollout in the EU is planned over coming weeks. Approved researchers can apply for detector access.
Why it matters
A generation-time signal gives platforms another way to investigate synthetic text without requiring visible labels, but its value depends on false-positive controls, editing resilience and detector governance.
What to do
If eligible, test short and long outputs, paraphrases and mixed human text against a blinded set. Keep watermark detection as one signal, document thresholds and provide a human appeal path.
Caveat
OpenAI says heavy editing and short outputs can weaken detection, while some human text can be falsely flagged. The rollout is phased and the detector is not public.