As part of today's build, Microsoft is adding an orange indicator to the Windows Update icon in the notification area (system try) which is meant to alert users when they need a reboot. There's also a refreshed landing page for Search, which is part of Microsoft's ongoing campaign to separate and improve the Search and Cortana interactions in Windows 10.
Microsoft added icons for Power and User menus to its Start screen with this build as part of its Fluent design push. There's a new option in Date & Time Settings for manually synchronizing a PC's clock with the time server. Microsoft also added to the new mic icon the ability to see which app is using a PC's microphone.
Microsoft also added the ability to switch directly to Microsoft To-Do inside the Mail and Calendar application that's built into Windows 10 with today's build.
Microsoft officials are reminding Insider testers today that Insider preview builds are time-bombed. Insiders in the Fast and Slow rings need to be on the latest builds offered to those rings in order to avoid hitting the timebomb. For Fast Ring testers, the timebomb is set to December 14. Slow Ring testers need to be on Build 17763 (the final October 2018 update build) to avoid hitting the timebomb. Those using ISOs for Build 18272 need to be on Build 18290.