Following release of iOS 9.0.2, Apple stops signing iOS 8.4.1 and iOS 9.0
Following the release of iOS 9.0.2 for iPhone, iPad, and iPod touch this morning, Apple has closed the signing window for iOS 8.4.1 and iOS 9.0. This means that users can no longer downgrade from a more recent version of the operating system to either of those older builds.