Microsoft releases Windows 10 Insider Preview Build 14926 for mobile and PC to insiders on the fast ring. Microsoft has made it so that Insider preview builds now have an expiration date. Starting tomorrow, September 15th, users of older builds will start seeing expiration notices once a day. Then on October 1st, the PCs will start rebooting every three hours and finalyl on October 15th will not boot at all. Microsoft also added an experimental Snooze action on a tab in Microsoft Edge which provides you with a way to set a Cortana reminder on the website you are viewing.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-insider-preview-build-14926-released-with-build-expirations/