As is par for the course, Apple has stopped signing a previous version of its mobile operating system, iOS, now that a newer version has been released to the public.
Today, Apple has officially stopped signing iOS 11.3, thanks to the public launch of iOS 11.3.1 in late April. Now that iOS 11.3 is no longer being signed by Apple, this means folks out there in the wild won’t be able to downgrade to the software from iOS 11.3.1. This impacts folks with jailbroken devices more than anything else, but if someone were running into bugger software with the latest release, up until today they could have downgraded to the previous public version of iOS.
Last week, Apple released iOS 11.3.1 to the public, which offers the standard performance boosts, behind-the-scenes tweaks and improvements, but primarily focused on fixing third-party display repair issues that had cropped up recently. That version of the software is available to download and install now on supported devices.
Meanwhile, looking ahead, Apple is currently in the process of beta testing iOS 11.4, which is the next big update planned for the mobile OS. The new release is currently being used to test Messages in iCloud, among other things. There is no definitive launch date for that software just yet.