It was a secretive program — it wasn’t advertised anywhere, and we had to sign an NDA about its existence (which we have since been released from). I got the impression that this was because OpenAI really wanted to keep the existence of GPT4 under wraps. Anyway, that means I don’t have any proof beyond my word.

OpenAI did this too, with GPT-4 pre-release. It was a small program, though — I think just 5-10 researchers.