iOS 8 adoption keeps climbing though not as rapidly as iOS 7 did over the same period last fall.
Data released by mobile analytics firm Mixpanel showed iOS 8 with an adoption rate of 44.5 percent as of Monday -- 20 days post-launch. That leaves iOS 7 with nearly 51 percent of Apple's mobile device users -- and older versions of Apple's mobile OS with a collective percentage of around 4.5 percent.
Apple released iOS 8 to the public on September 17. Within less than a day, the, according to Mixpanel. By September 19, that number had climbed to 21.6 percent.
But iOS 8 still trails its predecessor in popularity.
On September 18, 2013, when iOS 7 launched, Mixpanel reported an adoption rate of about 15 percent before the day had even ended. By October 7, 2013 -- 20 days post-launch -- iOS 7 had achieved an adoption rate of 69.7 percent, according to Mixpanel.
Mixpanel's data is based on its analysis of mobile-app usage.
"We get data from users using our customers' apps and heavily anonymize it," a company spokesperson told CNET in September. "We work with thousands of apps and that means tens (of millions) to hundreds of millions of users across all kinds of devices."
Fellow analytics firm Fiksu shows an even lower number for iOS 8 at this point. As of Monday, Fiksu's stats point to a 37.2 adoption rate for Apple's latest mobile OS.
Based on visits to the App Store, Apple's own stats paint a different picture than do Mixpanel and Fiksu. On September 21,, iOS 7 with 49 percent, and older versions collectively with 5 percent. Those numbers measure only devices that visited the App Store on September 21 and would certainly be much higher at this point per Apple's own analytics.
What could account for the slower uptake of iOS 8 versus iOS7? Last year, iOS 7 offered a radically new look and feel for Apple's mobile OS. This year, iOS 8 offered no such radical changes in its interface, instead throwing in some new apps such as Apple's Health app and a few useful but not necessarily groundbreaking tweaks.
iOS 8 has also been plagued by a series of technical woes. On September 24, Apple released iOS 8.0.1 to fix some bugs in version 8.0. But 8.0.1 was even more bug-ridden than the original version, forcing Apple tountil it could correct its snafu. Released on September 25, appears to be much more stable at this point, however, some users are still complaining of connectivity issues and other problems.