Starting tomorrow September 15th, PCs running really old Insider Preview builds will start to see build expiration notifications once a day. Then on October 1st, these PCs will start rebooting every 3 hours and then on October 15th – these PCs will stop booting all together. If your PC is running one of these old Insider Preview builds, please make sure you update to Build 14926 via Settings > Update & security > Windows Update. Build 14926 has an updated expiration date of May 1st, 2017. If your PC is running the Windows 10 Anniversary Update (Build 14393) in the Slow and Release Preview rings today – this does not apply to you and you will not be notified of your build expiring.