In the API that is an explicit option, as well as in the paid consumer product as well. The amount of business that they stand to lose by maliciously flouting that part of their contract is in the billions.
I can't remember the last time a tech company has collected less data than they admit.
If you read the privacy policies you agree to, they have access to everything and outright admit it will be logged. That API option is merely a request, and absolutely need not be respected.
I can't believe we're still doing this rigamarole. If the product is not specifically designed, engineered, and open-sourced to be as privacy protecting as possible and it's not literally running on a computer you own, you have zero expectation of privacy. Once this has been proven 1 million times we don't need to prove it anymore, we can just assume and that's a very reasonable assumption.
Isn't the only way to do that is for ChatGPT to run locally on a machine? The moment your chat hits their server they are legally required to store it?