Microsoft was planning to launch its next major Windows 10 update, codenamed Redstone 4, last week. The software giant had targeted April 10th as an internal target to release the update, 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) 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.

Video: hear Microsftie say "Windows 10 April 2018 Update" pic.twitter.com/H4WPkCC3sA — WalkingCat (@h0x0d) April 17, 2018

The next major Windows 10 update will include features like Timeline, HDR support, dictation, and even more Fluent Design changes. Microsoft is now testing its next update, codenamed Redstone 5, that will be available later this year. Tabbed apps will feature heavily in this update, and we’re expecting to hear more about new features at Microsoft’s Build developer conference in May.