Have you read anything about the feature?

They’re asserting that all the audio is done on device, and the results of encrypted so they can’t access them even from the backups.

Unlike… EVERY… other tech company, it is in Apple’s interest to be privacy-focused.

Even if you just have to believe them, which you do pretty much, they’re the biggest name pushing for privacy in the world right now. They make more on selling devices than they make on ads and behaviors. It’s in their interest to not lie.