While iOS 9 has been growing at a very steady pace, a leap by over 20% is certainly questionable. However if you suspect that there might be some cheating going on, there isn’t. Instead it has been suggested that the leap to 57% is courtesy of the new iPhone 6s and 6s Plus, both of which has sold pretty well since its release.
In fact according to Apple’s previous numbers, they were boasting 13 million units sold over its opening weekend, and this is just the markets that it was originally available in, so safe to say that we expect even higher numbers once the iPhone 6s and 6s Plus become available in other markets around the world.
In the meantime just to give a bit of perspective, iOS 8 only managed to hit 56% about two months after its release, versus iOS 9 which seems to have achieved that with it only being released less than a month ago.