With just hours before Apple announces new iPhones, an ad network trolling its traffic data said that iOS 7, which will be replaced next week on most customers' devices, was running 90% of all North American iPhones and iPads.

Read our full iOS 8 review

The uptake on iOS 7, which was released Sept. 18, 2013, had reached 90% of all iOS devices in the U.S. and Canada by Aug. 31, according to Chitika. The online ad network regularly mines its data to publicize statistics about operating system and browser usage.

Like Irish metrics vendor StatCounter, Chitika's numbers are best described as "usage share" since the firm measures how active users of a specific OS are on the Web. Because both StatCounter and Chitika tally usage, not users, the numbers may have no relation to the "user share" -- analogous to the installed base -- which other analytics companies, like Net Applications, tout.

Unlike Google's Android or Microsoft's Windows Phone, iOS bypasses mobile carriers and is delivered directly from Apple to customers. Cupertino's practice has always resulted in faster uptake by users. Android 4.4, aka KitKat, was released in October 2013, but currently accounts for only 21% of all versions of Android, for example.

Within a week, over half of all North American iPhone and iPad users had upgraded to iOS 7.

"It only took a week following the release of iOS 7 for the majority of iOS traffic to be coming from that version, so the release of iOS 8 can reasonably be expected to elicit a similar reception," said Chitika yesterday.

iOS 8 will run on 2011's iPhone 4S and later, and on the iPad 2 and later.

If Apple follows past practice, it will demonstrate several iOS 8 features today, probably adding to those it touted three months ago at the Worldwide Developers Conference (WWDC), Apple's annual developers confab, then release the operating system to the public on Wednesday, Sept. 17, two days before the new iPhones go on sale.

Apple will kick off its iPhone and iOS 8 event at 10 a.m. PT (1 p.m. ET), and for the first time for an iPhone roll-out webcast the event live. The broadcast will be streamed from Apple's website.