As it turns out, Apple realistically needs customer data to make Siri AI work well. So, starting with iOS 27, it is asking users to opt-in to training on your data.

Apple wants your Siri conversations

Apple wants your Siri conversations
A new section in the iOS 27 privacy policy shows that Apple has reversed its stance on using customers’ data to train its AI models. Previously, the company assured customers that it had no need for customer data, and would figure out how to make Siri AI work well without it.
Apple maintains that it “takes steps to ensure that personal data is not stored or used by Apple.” But as Heise points out, and Apple has said in the terms of service for a few years now, the audio material may be listened to by Apple employees after anonymization.