Microsoft was planning to launch its next major Windows 10 update on April, but a last-minute “blocking bug” delayed the release. In an unusual change, Microsoft has now issued a new build instead of fixing the bug with a cumulative update via Windows Update. 

“In certain cases, these reliability issues could have led to a higher percentage of BSOD (Blue Screen of Death) on PCs for example,” says Microsoft’s Dona Sakar. “Instead of creating a Cumulative Update package to service these issues, we decided to create a new build with the fixes included.” Microsoft has not revealed the exact reason for the blocking bug, or why it was discovered at the last moment.

The new build is available to Windows Insiders in the Fast Ring, and will be made available to Slow Ring and Release Preview shortly. Sources familiar with Microsoft’s plans tell The Verge that this build (version 17134) has now been marked as the final version of the next major Windows 10 update.

Microsoft has still not officially named this update, despite the company using the Spring Creators Update naming multiple times. It now appears Microsoft will choose “Windows 10 April 2018 Update” as the final name for Redstone 4. Microsoft watcher WalkingCat has discovered a video referencing this name, but the blocking bug delay could push the release of this update into May — further complicating the naming of this update.

Adding more features to Sets

Microsoft is adding more functionality to its Sets windows-management feature, with the latest Windows 10 'Redstone 5' test build.

Build 17639, which is available on April 4 to "Fast Ring" Insider testers, adds several new Sets features. Sets is a windows-management tool that allows users to group together web pages, documents, files, and apps and work with them in tabs in Microsoft's Edge browser.

With this build, drag-and-drop app tabs within and between Sets now works. With 17639, users can use Alt + Tab to switch between groups of tabs. There are new Settings for Sets with this build, and Microsoft is working to make getting two File Explorer windows grouped together. In addition, there is a new UI for more easily opening new tabs and windows in the File Menu.

Microsoft's blog post on 17639 itemizes some other new Sets functionality, fixes and known issues. The blog post also mentions that Microsoft is planning to enable Sets for more Win32 desktop apps, including Office (no timeframe provided), and this will be available to test for those who are in the Officer Insider program and running the latest Office builds.

Redstone 5 is due to roll out starting in October 2018, if Microsoft continues to stick to its stated Windows 10 rollout schedule.