If you’re already running the technical preview build 9879 for Windows 10 and would like to receive the January Technical Preview set to come out by the end of the month, you’ll need to an upgrade with a very complicated name (KB3025380). Microsoft’s summary of the upgrade states “This update includes improvements to Windows 10 Technical Preview Build 9879 that will let members of the Windows Insider Program continue to receive future released builds of Technical Preview.”
While upgrades to the technical preview range from bug fixes to new features, the January technical preview is a new build and as such will have a bevy of new additions. Features include continuum which allows 2-1 devices to easily switch between touch and keyboard interfaces, Cortana on the desktop, and an overall cleaner layout. The recently announced project Spartan will not be available as part of the January technical preview but some features of it will be.