Windows 11 26H2 Release Preview Build 26300.9278 Now Available

Microsoft has pushed Windows 11 build 26300.9278 to the Release Preview channel for Insiders, marking the arrival of version 26H2. This update matters because it establishes the servicing foundation for the upcoming major release while sharing the same branch as versions 24H2 and 25H2. Users who need to test new features before the general public can now access this preview tier on their current hardware. The release provides a stable environment for evaluating changes before they roll out to the broader Windows 11 user base.

Microsoft ships the servicing foundation for the next major Windows 11 version to testers

The core of this release is the introduction of Windows 11 version 26H2, which Microsoft confirmed will share the servicing branch with versions 24H2 and 25H2. This structural alignment means that the update path for 26H2 follows the same technical framework as the previous two major versions. Insiders receive early access to these changes through the Release Preview ring, allowing them to identify potential issues before a wider deployment. The build serves as the primary vehicle for delivering these upcoming features to a controlled group of testers.

Microsoft provides two methods for installing this update on compatible systems. Users can upgrade by downloading the eKB or enablement package directly through Windows Update. This method integrates the installation process into the standard update workflow for existing Windows 11 installations. The company also confirmed that standalone ISO files for this update will become available in the near term. These ISOs offer an alternative installation path for users who prefer manual deployment or clean installs.

An optional preview update for August 2026, identified as KB5120998, was released alongside the main build. This optional component allows users to preview specific fixes or features that are not part of the core enablement package. We looked at the last Windows 11 update earlier while tracking broader changes, and several of the same balance and stability themes came up in this release. The combination of the main enablement package and the optional August 2026 update provides a comprehensive preview experience for testers.