Siri was never a stand-alone App. It was the flagship feature for the launch of the iPhone 4S and was fully built-into iOS. I remember this very clearly.Siri initially launched as a stand-alone app on the app store before Apple bought it and integrated it into the OS and made it online-only so they could make it smarter.
It was partly based on technology from an App which Apple had acquired. But that App was different from Siri (not just the name, the functionality as well).
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