Apple released iOS 11.4.1 on July 9th brining performance improvements to users. Today 9 days later and Apple has stopped signing iOS 11.4 meaning users can no longer downgrade.

Apple is currently only signing iOS 11.4.1 and beta testing iOS 12. At this point it is unclear if we will see any further iOS 11.x, iOS 12 will be made available to the public later this year.