Adoption of Apple's iOS 10 already at 15% in early tracking data

iOS 9 usage is down to 80.86 percent from a Tuesday peak of 92.81, noted analytics firm Mixpanel. Some 4.29 percent of iOS users are still running iOS 8 or earlier, whether because of device limitations or otherwise. iOS 10 almost instantly eclipsed pre-iOS 9 devices after the software's Tuesday release.

A year ago, iOS 9 managed to reach 12.6 percent of devices in its first 24 hours — similar to results for iOS 8 in 2014.

It's not clear why iOS 10 is seeing a higher conversion rate. While people may be tempted by the software's features, such as a better notification system and enhanced Messages app, other factors could be involved.

More people may be using compatible hardware for instance, and iOS 9 introduced easier over-the-air updates — the software can temporarily delete installed apps to clear space, then restore them when an upgrade is complete.