Now only iOS 12.
As we warned last week, October 9, Apple stops issuing digital signature to the iOS 11.4.1. This means that iOS 11.4.1 it is no longer possible to install or downgrade to it from iOS 12.
Apple stopped signing iOS 11.4.1 three weeks after the final versions of iOS 12. This time should be long enough to ensure that everyone was able to come back from iOS 12 to iOS 11. Now return to iOS 11 more impossible.
For Apple this practice is common, as we warned last week. It is important to emphasize that the installation of iOS 11 is now impossible in any way — workarounds system protection Apple does not exist. At least on devices without jailbreak, which there is no 11.4.1 for iOS, not for iOS 12.
In fairness it should be noted that iOS 12 iOS 11.4.1 superior speed and stability. The only problem iOS 12 is not the highest battery life of the iPhone and iPad. However, increase noticeably at this and this methods.