The update, which became available for download Monday, adds support for Apple Pay, brings back the camera roll and launches the iCloud photo library.
The percentage of users updating to Apple's latest mobile OS has remained virtually flat since September 21, which was four days after its release.
A mobile analytics firm pegs iOS 8's adoption rate at 44.5 percent since launch 20 days ago. By contrast, iOS 7 had reached nearly 70 percent adoption over the same period last fall.
The latest version of Apple's mobile OS isn't yet gaining the traction that its predecessor did last year. Why might that be?
Following its official launch Wednesday, Apple's new mobile OS has already shot up the ranks, according to mobile analytics firm Mixpanel.
Apple may test the waters of a sapphire-screened phone by limiting the tough but pricey material to a single version of the next iPhone this year, claims analyst Gene Munster.
Chief Financial Officer Fran Shammo says he "feels much better about the second quarter."
The company already says Edge adoption is running above expectations, although it didn't disclose any numbers.
The phone's screen would curve to conform to its rounded corners, according to Japanese website Macotakara.
Some retailers have shied away from Apple's mobile payments service, and the equipment needed by supported industry players won't pop up overnight.