iOS 9 was installed on an estimated 12.6 percent of all iOS devices just 24 hours after its release. That showed, at the time, a slightly slower uptick in adoption than iOS 8 and a much faster upgrade path than competing operating systems, such as Android. On Monday, however, Apple confirmed that consumers are adopting iOS 9 faster than any other iteration of the mobile operating system.

"Apple also announced the fastest iOS adoption ever, with more than 50 percent of devices already using iOS 9," Apple said. Apple's senior vice president of worldwide marketing Philip Schiller also sounded off on the release. "iOS 9 is off to an amazing start, on pace to be downloaded by more users than any other software release in Apple's history," Schiller said.

Apple noted that it has received an "incredibly positive" response to its new iPhone 6s and iPhone 6s Plus, which will begin to land in consumer hands on Friday, September 25.