Following close on the heels of the May 29 release of iOS 11.4, Apple has stopped signing iOS 11.3.1, which was the previously publicly released version if iOS.
This means that if you’ve upgraded to iOS 11.4 on your iPhone, iPad, or iPod touch device, there’s no going back. Users will be unable to downgrade to the earlier version of iOS.
This is a routine move for Apple, which usually does this a week or so after a new iOS operating system update, in an effort to encourage users to keep their iOS devices up-to-date.
iOS 11.4 is the only version of Apple’s mobile operating system that is available for use by the general public. However, developers now have access to iOS 12, which is currently in beta testing, and will be released to the public in the fall.