What You Need to Know About Apple's Siri Data Retention
"If you turn off Siri, Apple will delete your User Data, as well as your recent voice input data," Apple’s privacy statement reads. "Older voice input data that has been disassociated from you may be retained for a period of time to generally improve Siri and other Apple products and services."
Pressed for clarification, Apple spokesman Trudy Muller told Wired that each time you speak to Siri, that information is transferred to Apple's servers for analysis. Apple then generates random numbers to represent the user and associates voice files with that number. It bears repeating that it's a random number and not your Apple ID or email address.
Apple holds onto your the voice recording for six months, after which time it "disassociates" and deletes your user number from the voice file. However, those disassociated files are still stored for up to 18 additional months. Why? Apple claims it uses them for product testing and to improve Siri.