Apple announced Monday that iOS 9 adoption has already topped 50 percent, just a few days after it was released. While Apple always enjoys best-in-industry adoption rates for its operating system updates, the company said this is the fastest adoption ever.
The comment came as a one-liner in a press release about iPhone 6s and iPhone 6s Plus availability on September 25th: "Apple also announced the fastest iOS adoption ever, with more than 50 percent of devices already using iOS 9."
Apple's developer site said that iOS 9 adoption was measured at 52 percent as measured on the App Store on September 19th, 2015, as shown in the chart below.
iOS Adoption Rate Chart from Apple's Developer Connection
For comparison, Android's largest installed base is KitKat, Android 4.4, which is two-versions old and was released in November of 2013. Google's Android Dashboard said that KitKat installations represent 39.2 percent of devices visiting Google Play. Lollipop (Android 5.0 and Android 5.1) represent 21 percent of installations, and was released in November of 2014.