OpenAI APIs have pretty much as clear a contract as you can get with a third party.
> Starting on March 1, 2023, we are making two changes to our data usage and retention policies:
> OpenAI will not use data submitted by customers via our API to train or improve our models, unless you explicitly decide to share your data with us for this purpose. You can opt-in to share data.
> Any data sent through the API will be retained for abuse and misuse monitoring purposes for a maximum of 30 days, after which it will be deleted (unless otherwise required by law).