{
"title": "Windows 11 Optional Week D Previews: KB5089573 & KB5089570 Explained",
"summary": "On May 26, 2026, Microsoft pushed out optional Week D preview updates for Windows 11 24H2, 25H2, and 26H1. KB5089573 bumps 24H2 and 25H2 to builds 26100.8524 and 26200.8524, while KB5089570 targets the newer 26H1 version. These previews contain non-security fixes destined for the June Patch Tuesday release.",
"meta_description": "Microsoft released optional Week D previews KB5089573 and KB5089570 for Windows 11 24H2, 25H2, 26H1 on May 26, 2026. These updates raise builds to 26100.8524 and 26200.8524, with KB5089570 targeting 26H1. Learn what's inside and whether to install.",
"content": "Microsoft has rolled out its Week D optional preview updates for Windows 11 on May 26, 2026, delivering KB5089573 and KB5089570 to users running versions 24H2, 25H2, and 26H1. These updates are part of Microsoft's monthly servicing cadence, released during the fourth week of the month (hence \"Week D\") to give IT administrators and enthusiasts a sneak peek at the fixes and improvements slated for the next Patch Tuesday. While not mandatory, they offer a chance to validate upcoming changes before they roll out broadly.
KB5089573 bumped Windows 11 24H2 and 25H2 to build numbers 26100.8524 and 26200.8524, respectively. The companion update, KB5089570, targeted the newer 26H1 branch, though precise build details for that version were not fully outlined in early notices. These builds reflect incremental quality improvements over the previous releases, typically addressing performance, reliability, and compatibility issues that have bubbled up since the last cumulative update.
What Exactly Are Week D Preview Updates?
Windows servicing follows a predictable rhythm. Each month, Microsoft releases a mandatory security update on Patch Tuesday (the second Tuesday), labeled as the \"B\" release. The \"C\" and \"D\" weeks (third and fourth weeks) often see optional non-security previews—C for older Windows versions, D for the latest Windows 11 releases in recent cycles. These previews contain the non-security content that will eventually be bundled into the following month's B release, giving users and organizations a chance to test drive the fixes.
Optional updates are not automatically installed via Windows Update unless users actively seek them out by clicking \"Check for updates\" and then downloading the specific preview. They are also available from the Microsoft Update Catalog for manual download. This opt-in nature means only those who want early access—or need to validate a particular fix for a line-of-business application—tend to install them.
The Week D designation gained prominence with Windows 11, as Microsoft streamlined its update naming to align with calendar weeks. For enthusiasts tracking every build number bump, these previews are a regular fixture on the last Tuesday or Wednesday of the month.
Breaking Down KB5089573 and KB5089570
The May 2026 Week D releases bring two main packages:
- KB5089573 targets Windows 11 version 24H2 and 25H2. After installation, version 24H2 moves to OS Build 26100.8524, and version 25H2 moves to 26200.8524. These four-digit build extensions (the .8524 part) indicate the cumulative patch level atop the base feature update.
- KB5089570 is aimed at version 26H1, the latest feature update presumably just released or in preview. The exact new build identifier for 26H1 was not immediately disclosed in the available excerpts, but it will follow the same pattern of adding a patch number to the base build of that version.
Understanding Windows 11 Build Numbers
Each Windows 11 feature update has a base build number. For 24H2, it's 26100; for 25H2, it's 26200; for 26H1, presumably something like 26800 or similar (though not confirmed). The four-digit suffix after the dot represents the monthly cumulative patch. The first few digits in that suffix often denote the month or serial number of the cumulative update. So, for example, .8524 might indicate the 85th cumulative package for that version. This numbering allows precise tracking. Servicing stack updates (now combined) also increment the build. By inspecting the build, IT pros can verify that a particular fix is included.
What's Inside? (Hint: No Specifics Yet)
At the time of this writing, Microsoft had not published detailed release notes or knowledge base articles for KB5089573 and KB5089570. The lack of immediate documentation is not unusual; optional previews sometimes ship with succinct initial notices, while the full update history page is fleshed out within a day or two. Historically, these D-week previews include:
- Quality improvements to the servicing stack (the component that installs updates).
- Bug fixes for issues reported by users or detected via telemetry—covering areas such as printer connectivity, audio glitches, display scaling, Start menu reliability, and File Explorer quirks.
- Compatibility updates for drivers and third-party software.
- Minor tweaks or additions to existing features, such as updated app icons, network flyout improvements, or less intrusive notification prompts.
Because the community discussion thread provided for this article was empty at press time, real-world feedback from early adopters is still pending. In past D-week cycles, Windows enthusiasts on forums have been quick to report any regressions—such as slower startup, broken VPN connections, or app compatibility snags—as well as successful improvements. We will update this coverage if significant user reports emerge.
How to Get the Updates
If you're eager to try these builds before the June Patch Tuesday (likely June 9, 2026), you can manually trigger the download:
- Open Settings > Windows Update.
- Click Check for updates.
- When the optional preview appears (it may be labeled as \"Cumulative Update Preview for Windows 11… (KB5089573)\" or similar), click Download and install.
- Restart your PC after the installation finishes.
Remember, these are previews, so they are not force-installed. If you skip them, you'll get the equivalent content as part of next month's mandatory Patch Tuesday update.
Should You Install Optional Updates? A Balanced View
The decision to install Week D previews hinges on your risk tolerance and needs.
For IT administrators and power users: Early testing can reveal quirks that might affect critical line-of-business applications. If a fix addresses a persistent bug in your environment, grabbing the preview may resolve it sooner. Just ensure you test on non-production machines first.
For everyday consumers: If your system is running smoothly and you don't have a specific problem listed in the preview's release notes (once published), it's usually safer to wait for the Patch Tuesday release. Optional previews, by their nature, have undergone less testing than the final B update, so they occasionally introduce new instabilities.
A word on build numbers: The jump from 26100.xxxx to 26100.8524 indicates a significant number of cumulative changes since the last public build for 24H2. Each patch number increment represents a compilation of hotfixes. The higher the final digits, the more patches that update contains. This incremental build numbering helps Microsoft and enterprise users track exactly which fixes are installed.
Common Pitfalls with Preview Updates
While most optional updates sail through without incident, a few recurring themes have plagued past releases:
- Printer Headaches: A recurring theme in Windows optional updates is printer-related issues. Whether it's Type 4 drivers, network printers disappearing, or the infamous \"hold\" that Microsoft sometimes places on upgrades, printer compatibility is a frequent pain point.
- Audio Driver Glitches: Realtek, Conexant, and other audio chips sometimes lose functionality after a cumulative update.
- Customization Reset: Rarely, user settings for default apps, taskbar configuration, or file associations may reset.
- BSODs: Though uncommon, a bad driver interaction can cause blue screens. Microsoft usually pulls an update quickly if that's reported.
Windows 11 Version Landscape in Mid-2026
The introduction of three active feature versions—24H2, 25H2, and 26H1—signals Microsoft's accelerated release cadence. With Windows 11, the company has moved away from the old twice-a-year feature update schedule to a more flexible model that can push out significant new versions when ready. However, each version maintains its own servicing branch, so cumulative updates like KB5089573 and KB5089570 are tailored to specific base builds.
Version 24H2, being the oldest, likely has the broadest installed base and the most mature servicing. Version 25H2 may have brought AI-powered features or shell enhancements. Version 26H1—if it followed the pattern—might be a mid-cycle feature drop that doesn't reset the support lifecycle but adds incremental capabilities. Microsoft's documentation typically clarifies these details upon official announcement.
As always, business users on Long Term Servicing Channel (LTSC) releases will not see these D-week updates for their specific versions, as LTSC follows a separate servicing track detached from these optional monthly previews.
The Silent Launch and the Waiting Game
One oddity of this May 2026 Week D release is the apparent silence from official channels. At the time this was published, the Windows 11 update history page and the official Microsoft KB articles were not yet updated with detailed release information. This quiet rollout occasionally happens when updates first publish to Windows Update servers before the web documentation team updates their pages.
For now, the only tangible data points are the KB numbers, the target versions, and the resulting build strings. Enthusiasts who have already installed the updates may be digging through event logs and system files to uncover changes. In previous cycles, such early birds have spotted:
- Updated inbox apps (like Notepad, Paint) being refreshed via the Microsoft Store.
- Tweaks to the taskbar search box behavior.
- Under-the-hood kernel performance adjustments.
- Fixes for Bluetooth audio stutter that plagued some devices.
The Insider Connection
These public previews are distinct from Insider builds. Insiders in the Dev, Beta, and Release Preview channels get even earlier builds. The D week updates are essentially the Release Preview ring's final output before wide deployment. This means that the fixes in KB5089573 and KB5089570 have likely been tested by Release Preview Insiders for a week or two. So, by the time the public sees them, they've already been vetted by a smaller, more adventurous group. The lack of major incident reports from Insiders is a good sign, though specific threads on Reddit r/windowsinsiders may offer clues.
What Comes Next?
After the optional preview settles, Microsoft will compile any final hotfixes and release the combined security + quality update on the June Patch Tuesday. That mandatory update will include everything from these previews, plus any critical security patches that weren't ready in time for May. For regular users, waiting ensures you get the most stable bundle.
The absence of community discussion in this article's source material means we cannot gauge the initial response. Typically, platforms like Reddit, Microsoft Community, and tech forums light up with threads dissecting these optional updates within hours. If you have installed either KB5089573 or KB5089570, consider sharing your experience in the comments or on your favorite Windows forum—your feedback helps map the real-world impact.
Microsoft's approach to transparency with preview updates has improved over the years, but it still falls short of real-time clarity. The lag between deployment and documentation can be frustrating for IT managers who need to decide quickly. Until official KB articles appear, the best guidance is to