Microsoft has rolled out yet another update to Windows 10 build 9879, which is the latest build currently available via the Windows Insider Program. This update simply prepares your system to allow for the download of the next build, which is expected in January (known as the January Technical Preview).
Microsoft revealed recently that they've got an exciting build to share in January, as part of the focus on consumers. It'll be part of the FBL_AWESOME branch and will include a ton of UX changes and new features. This update is rolling out now and is available via Windows Update.
Hi #WindowsInsiders - one more WU update today. This one preps your system to take the next build from FBL_AWESOME branch.
— Gabriel Aul (@GabeAul) December 18, 2014
However, there is just one slight problem. Build 9901 was leaked not too long ago, so if you managed to download and install it, you will not be able to upgrade to the newest build in January. It is recommended that you install build 9879 from the Windows Insider Program and wait for Microsoft to release the new build in January. The ability to upgrade to newer builds is broken in build 9901.