After less than three months on the market, iOS 7 is installed on some 74 percent of devices connecting to the App Store, according to a chart posted on Apple's App Store support page for developers.
The company puts iOS 6 adoption at 22 percent, and older OS versions at just 4 percent. The data from Apple is likely the most accurate adoption data we will see and is the most relevant for developers as its taken directly from the App Store.
For comparison, as noted by TechCrunch, the latest version of Android -- KitKat -- only reports a 1.1 percent adoption rate.
Article Link: Apple's App Store Usage Numbers Suggest iOS 7 Adoption at 74%