Windows: Trying out Windows Insider builds is an awesome way to stay on the bleeding edge. If you don't update those builds though, Microsoft will deactivate them. The first round of expiration dates are coming up. If you're still on the earliest Windows 10 Insider builds, you'll start seeing some nag screens today warning you that you need to update soon. Starting on October 1, those builds will start rebooting every three hours. Finally, on October 15, those builds won't boot at all. Microsoft hasn't clarified which builds will get these nag screens aside from saying they're "really old builds".
Of course, the easy way to avoid this is to update. Insider builds are always free, so there's no cost to doing so. You can also defer upgrades and switch to the slow update channel to minimise risk to your machine. Eventually, though, you'll have to stay updated.
Announcing Windows 10 Insider Preview Build 14926 for PC and Mobile [Windows Insider Blog via Ghacks]