I was hoping there was a functional design or overview document for Siri that describes how it works and what resources it requires.
AFAIK such a document does not exist. However, if your primary concern is offline processing, that’s pretty easy to test: turn off your Mac’s networking and see how far you get with Siri.
Are there any 3rd party libraries/frameworks that are alternatives.
There are various third-party speak recognition libraries out there — some of which require the Internet and some of which don’t — but I don’t have any experience with them so I can’t make a concrete recommendation.
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Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"