Within the first twenty-four hours, iOS 8 update appeared to be slower than its predecessors.  A few weeks in, this continues to be the case says analytics firm Fiksu.

After twelve days, both iOS 6 and iOS 7 had comfortably crossed the 50% mark for iOS usage. By contrast, iOS 8 is yet to hit the 40% mark according to Fiksu’s measurements. An independent study from Mixpanel says iOS 8 is closer to 50%, but it is still far behind iOS 7’s rate of uptake.

At least, iOS 8 is ahead of iOS 5 in terms of usage, which should be expected given that iOS 4 users wanting to upgrade to iOS 5 had to plug in to iTunes to update. Since that change, both iOS 6 and iOS 7’s upgrade rates were almost double that of iOS 5. For reasons not fully known, iOS 8 currently sits about halfway between these two.

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Meanwhile, iPhone 6 adoption is record-setting. The graph above shows iPhone adoption (as a percentage of total iPhones in use) in the days after release. The iPhone 5 and iPhone 5s followed near-identical growth path, but the iPhone 6 is more than double that rate. As of 17 days since release, the iPhone 6 has touched the 4% level. For comparison, the combined share of the iPhone 5s and iPhone 5c was about 3% in the same period.

That’s without adding in iPhone 6 Plus usage. Adoption of the larger 5.5 inch device appears to be slightly more than the iPhone 5c right now. From this data, both models of iPhone 6 crossed 5% of total iPhone usage in under 18 days. This is roughly twice the combined uptake of the iPhone 5s and iPhone 5c.

Note that these figures are all based on current iPhone usage. Although the information should be similar, in some cases, usage rates may vary wildly to sales. However, it is important to remember that in absolute units, the iPhone 6 and 6 Plus are exceeding iPhone 5 series devices even more, as the absolute base of phones is larger now than in previous years.

On an ‘official’ basis, Apple last updated its iOS adoption statistics on the 21st of September, saying that 46% of iOS users visiting the App Store were running iOS 8. Historically, this number is always greater than third parties numbers, as they track wider scope of usage characteristics beyond visits to the App Store.