I thought they already didn't use input data from the API to train; that it was only the consumer-facing ChatGPT product from which they'd use the data for training. It is opt-in for contributing inputs via API.

https://help.openai.com/en/articles/5722486-how-your-data-is...

That said, for enterprises that use the consumer product internally, it would make sense to pay to opt-out from that input being used.