Microsoft today released a new Windows 10 preview for PCs, the first build of 2016. The main focus of this build is structural improvements to OneCore, the shared core of Windows across devices.

Windows 10 is a service. As we wrote in our deep dive on how Microsoft is still building Windows 10, this means Windows Insiders are getting new builds even though the operating system launched in July 2015.

Gabe Aul, Microsoft’s vice president of the Engineering Systems team, explains the importance of this build:

The code refactoring and other engineering work we’ve been doing to optimize OneCore is nearing the point where we will be ready for teams to begin checking in new features and improvements. It will still be a few builds before any really noticeable changes show up, depending on when teams begin lighting up new features in their areas. We’re excited for Insiders to use this build to validate the work we’ve been doing to OneCore, so give this build a try and let us know of any issues you run into via the Windows Feedback app.

Aul also added that a known issue from the last build has been fixed. The progress dialog for copying or deleting files via File Explorer now shows up as expected.

Today’s update bumps the Windows 10 build number from 11082, made available to testers on December 16, to build 11099. The update should arrive overnight for testers (your PC has to be plugged in, and be on or sleeping). If you’re OK with bugs and want to get build 11099 now, head to PC Settings, select “Update and recovery,” then “Preview builds,” and click the “Check Now” button.

Microsoft plans to release new builds to testers more frequently in 2016. Although the operating system is becoming more stable, you can expect more bugs in the previews.