41% of the devices are still running an older version of iOS.
App Store support page has informed that the modern version of iOS is already running on 59% of the devices in use. iOS 11 grew from 52% in November, to 59% in early December, according to the stats, while the previous version (iOS 10) is now installed on 33% of the devices. Older versions of iOS are still on 8% of the active devices.
Despite the good growth, iOS 11 is slightly behind version 10 in terms of adoption rate. Back in 2016, iOS 10 reached a 54% share in November, while iOS 11 was 2 percentage points below iOS 10 on November 6.
Apple has already released a number of minor updates to iOS 11 to improve the performance and adds some new features. The current version 11.2 introduced Apple Pay Cash in the US, and many fixes and improvements. The last version also fixed the Calculator and Date bugs found in iOS 11.1.