Almost every serious customer is already using ZDR where nothing is retained at all, instead of "anonymized" data.

They already trained on pirated content, what makes you think they are going to honor ZDR?

A lot substance is hinged on the exact definition of the word "data" or "user data". In the age of post-truth everyone is claiming that they keep no "user data". Except that after running it once through some transformer program it's no longer "user data", it's something entirely else and these corpos gave ZERO promises regarding such laundered/transformed data at all, ever.

The guarantee on this is a (contractual) “trust me bro”, and a right to try to sue a multi-trillion-dollar company who will absolutely drive you into the ground with legal red tape.

If you are big enough to be able to withstand that, you’re already running (or trying to run) your own/open-weight models.

Just a thought experiment: considering training seems to be 'fair use', I wonder if they trained a tiny model to retain key info from your prompts, would mean that this would still constitute fair use, and allow them to legally claim they don't retain your data.

ZDR is based on the exact same pinky-promise as training opt-outs. There is no technical barrier to OpenAI, or whoever is running your compute, retaining your prompt after they run inference on their servers. If you don't control the hardware the model is being inferenced on, you don't control your data.

Where nothing is retained at all, allegedly.