Apple released iOS 12 September 17th, 2018 and I installed it right away on an iPhone 8 Plus and an iPad Pro. Installation went smoothly and there was a noticeable speed improvement on each device: apps launch faster, and the camera is ready to take a picture almost immediately.
iOS 12 will work on any iPhone that can run iOS 11. If you were waiting for iOS 11 to finally be ready for prime-time, forget it– instead, move to 12.
iOS 12 is not perfect; in a few days of medium use, the back button disappeared in the Settings app on my iPhone (I had to kill the app), and the Mail app quit on me once, on my iPad. But those things only happened once each, and the speed improvements are really nice. As usual, Apple is already working on an update and I look forward to installing iOS 12.1 (and then iOS 12.2).
Be aware that older, 32-bit apps will not run in iOS 12. You may recall seeing warnings saying “The developer of this app needs to update it” in iOS 10. If your device is using iOS 10, and you’re thinking of moving to iOS 12, and you’ve seen that warning about some app needing an update, take it seriously– any app that generated that warning in iOS 10 will not work in iOS 12. Of course, the app wouldn’t have worked in iOS 11 either, so if you’re on iOS 11 now, moving to iOS 12 won’t make it worse.
I’ll be posting articles here about the new features in iOS 12 soon. Meanwhile, if your iPhone or iPad is on iOS 11, go ahead with the iOS 12 upgrade. It’s a big improvement and you’ll know how to use it right away. if your device is on iOS 10 or older, be sure your apps will work before you upgrade. (You can check this on iOS 10.3 by going to Settings / General / About / Applications).