Over 60% of 9to5Mac readers are on iOS 8 following yesterday’s public release, but that’s not surprisingly representative of all users. In fact, adoption of iOS 8 this year seems to be lagging further behind previous releases, especially last year’s record setting adoption rate for iOS 7. A quick look at the various advertisers and research firms tracking adoption through apps and device usage on their platforms shows iOS 8 is sitting at around half of what iOS 7 had during the same time period.

Mobile marketing company Fiksu has iOS 8 adoption at 7.92% after the first 18 hours compared to 17% for iOS 7 over the same amount of time. Other stats show a similar slowing of adoption for iOS 8 versus last year’s iOS release. Researchers at Mixpanel have a live chart tracking adoption and note that it has iOS 8 adoption so far at just 14.25% compared to the almost 40% that iOS 7 had on its second day of release. Another live tracker from Appsee has similar stats as Mixpanel putting iOS 8 adoption at 13.1% at the time of writing. Tapjoy, on the other hand, is about to release data that has iOS 8 at just 5.90% after 18 hours on its network of apps with 200+ million unique iOS users per month. It also broke numbers down by platform with 6.60% iPhone, 3.96% iPad, and 7.65% iPods.

What exactly is causing the slower than usual adoption is unclear, but the stats are only slightly below past iOS releases apart from iOS 7’s record setting numbers. Perhaps the big jump in adoption numbers last year were due to excitement regarding Apple’s completely redesigned iOS 7 release. There’s also a possibility many users are holding off this year due to the higher amount of free storage needed to install — some users are required to have over 6GB of free space just to install iOS 8.

We’ll be keeping an eye on adoption and update if things pick up today.