Apple has stopped signing iOS 8.4.1 and iOS 9.0 following the release of iOS 9.0.2 earlier today.
If you want to stay on iOS 9.0 or 8.4 take care that you do not accidentally update because you won't be able to get back down. If you're still on iOS 8.4 and you do update you will not be able to jailbreak your device.