Just three weeks after the release of iOS 12, Apple's latest mobile OS already runs on most iPhones and iPads. According to data available on Apple's developer page, 53% of all iOS devices introduced over the past four years have run the latest iteration of iOS. When data sets are expanded to include iOS devices released before 2014, this adoption rate is still at a respectable 50%.
The numbers get even more impressive when we take iOS 11 into account. As shown in the figure below, 40% of iOS users on newer devices still run iOS 11. Looking at the cumulative number of iOS devices, iOS 11 controls 39%. In short, 89% of all iOS devices currently run an iteration of iOS that is at least about 1
As a point of interest, iOS 11 achieved adoption 65% about four months after the release. With iOS 12 adoption already at the 50% threshold, and with a massive refresh cycle to begin, the iOS 12 adoption is well on its way to surpassing iOS 11 adoption.
The above iOS charts are all the more impressive when we take a look at what's happening on the Android page. By Android Developer's dashboard, over 50% of all Android devices still run Android 6.0 Marshmallow or a pervasive version. Set differently, the majority of Android devices are running a mobile OS that is at least 3 years old. Overall, the rate of Android adoption has apparently improved in recent years, but it still pales compared to a new iOS edition.