You have been able to automatically install the app updates for some time, but there was no way to automatically install new system updates on your iPhone. To get a new iOS version on your device, go to Settings and download the update. It will either be instantly installed or you can install it at night. This whole process is easier in iOS 12.
Not mentioned in Apple's keynote at WWDC 2018, iOS 12 now offers the ability to automatically install new iOS updates instead of manually giving them each time. For those of you who wait before you upgrade to see if there are major issues with other users, this is probably not a setting you want to use. But if you do not mind jumping into a new update first, it makes it easy.
To test, make sure you are using the beta version of iOS 1
While there is not much information about this setting, it will likely require your iPhone to be connected to Wi-Fi and a power source to continue with an automatic iOS update, but that's not yet confirmed. It's also likely to be installed at night, similar to installing an iOS update that you later downloaded manually. And you'll probably need to enter your access code if you disconnect your iPhone afterwards as it will be needed anyway after a reboot.
But with that you're ready to receive updates as soon as they come in, what should be at least good for this beta phase. I have already experienced some bugs that are descended from the iPhone. Therefore, getting these patches sooner or later is a great help. Please note that your iPhone will be unusable for a few minutes while it installs the new iOS version, which means that services like the 911 will not work during that time.
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