Android
The oldest Android version Shake SDK works on is Android 5.0 Lollipop (API level 21), released back in June 2014. The newest supported version is always the latest publicly available Android.
According to stats, that means Shake supports 98.5% of Android devices worldwide.
iOS
The oldest iOS version Shake SDK works on is iOS 10, released back in September 2016. The newest supported version is always the latest publicly available iOS.
According to stats, that means Shake supports 99.0% of all iOS devices worldwide (and 99.9% of iPhones).