iPhone and iPad users still flock to download the latest version of iOS as it becomes available, but perhaps not as quickly as before.

According to Apple's developer portal, iOS 8 adoption now stands at 46 percent, while 49 percent of users are still on iOS 7. The remaining 5 percent are using “earlier” versions.

iOS 8 launched on Wednesday, September 17, which means the new version has been available for about six days. Apple didn't provide official data at this point last year, but several third-party metrics firms claim that uptake of iOS 8 has been slower than the previous version.

Mixpanel, for instance, claims that 33 percent of devices are using iOS 8 after six days, compared to 58 percent adoption for iOS 7 in its first six days. Both Tapjoy and Chitika also found that iOS 8 adoption was slower than iOS 7 in its first 24 hours.

The slower uptake could be due to several entwining factors. Some users may be deliberately holding off on the update due to its large size—the installation requires 5.7 GB of free space—or its tendency to run slower on Apple's oldest supported devices. Given that the iPad 2 and similarly-equipped iPad Mini are still Apple's most-used tablets, it wouldn't be surprising if those users are dragging down the numbers by avoiding an immediate upgrade to iOS 8. Meanwhile, both the iPhone 6 and iPhone 6 Plus are in short supply, preventing new buyers from getting on board with the latest operating system.

In any case, adoption of the latest iOS version is still much stronger than Android, where just 24.5 percent of users are on the latest version after nearly a year. Manufacturer-specific skins and wireless carrier involvement continue to slow down the upgrade process for Android phones, especially for non-flagship devices.

iOS users shouldn't have much cause for alarm. With nearly 50 percent of users on board with iOS 8, developers should have plenty of incentive to support the platform's newest features.