Checked against Microsoft's release notes · reviewed by human editors
KB5120998 is an optional preview update released on August 27, 2026, for Windows 11 version 24H2 and version 25H2. It updates your system to OS Build 26100.9278 or OS Build 26200.9278, bringing non-security fixes, quality refinements, and system reliability improvements ahead of the next scheduled monthly update. You can install it manually through Windows Update under optional updates.
Priya Natarajan
What's new in each Windows 11 cumulative update and feature release: what changed, what to expect, and whether to install it.
KB5120998 is an optional preview update released on August 27, 2026, for Windows 11 version 24H2 and version 25H2. It updates your system to OS Build 26100.9278 or OS Build 26200.9278, bringing non-security fixes, quality refinements, and system reliability improvements ahead of the next scheduled monthly update. You can install it manually through Windows Update under optional updates.
By Priya Natarajan
Fixes for updates that won't install, get stuck, roll back, or break something after installing.
KB5120998 is an optional preview update for Windows 11 versions 24H2 and 25H2. If it becomes stuck during download or fails to install, you can resolve the issue by running the Windows Update troubleshooter, clearing the SoftwareDistribution cache folder, or running SFC and DISM scans. Because KB5120998 is a non-security preview release, you can also safely pause or skip the update until next month.
By Maya Reyes
What changed and what broke, on the day Microsoft ships it.
Every guide shows the build it was tested on, or “verification pending” until an editor has checked it.
AI-assisted drafts checked against Microsoft’s release notes. No invented KB numbers, builds or error codes.