Microsoft pushed out optional preview cumulative update KB5089570 on May 26, 2026, bumping Windows 11 version 26H1 devices to build 28000.2179. The update bundles a handful of File Explorer improvements, security fixes, and under-the-hood changes ahead of next month’s Patch Tuesday.

IT admins and enthusiasts running the 26H1 feature update can now pull this update from Windows Update or the Microsoft Update Catalog. It arrives as a non-security preview, meaning it’s entirely optional and primarily meant for testing and validation in corporate environments. Home users who tick the “Get the latest updates” box will also see it offered.

Preview updates have been a staple of the Windows servicing model since Windows 10. They give organizations a chance to catch regressions before updates become mandatory during the monthly security release. With KB5089570, Microsoft is polishing several rough edges that snuck into the 26H1 rollout earlier this spring.

Build 28000.2179: What the Increment Tells Us

The jump from the previous public build to 28000.2179 is modest but significant. It confirms that the 26H1 release has settled into a stable cadence after its initial launch. Build 28000 itself is the RTM baseline for version 26H1, which started rolling out in March 2026. The .2179 cumulative patch includes all the fixes from previous updates plus new quality improvements.

Microsoft hasn’t published a complete changelog yet—that’s typical for preview updates. The company often details changes retroactively when the update becomes mandatory on Patch Tuesday. However, early reports and the sparse release notes highlight a few key areas of focus.

File Explorer Finally Gets Attention

The star of KB5089570 is a collection of File Explorer fixes. For months, users have griped about sluggish performance, context menu delays, and occasional crashes when navigating network paths. This update appears to tackle several of those pain points.

First, the File Explorer address bar now loads paths more predictably when mapping network drives. Previously, entering a UNC path could hang for seconds before resolving; build 28000.2179 cuts that delay significantly. Second, the dreaded “working on it” message that appears when opening large folders on slow drives has been reduced in frequency. Microsoft optimized the enumeration of directory contents, particularly for folders with thousands of mixed media files.

Dark mode inconsistencies in the File Explorer command bar also received a fix. In some scenarios, the background would flip to white while the rest of the window remained dark. This cosmetic bug has been squashed. Additionally, the context menu’s “Open in Terminal” option now reliably inherits the correct profile when Windows Terminal is the default console host.

Insiders who track Windows development closely will note that these aren’t brand-new features—they’re quality-of-life fixes. That aligns with the purpose of a preview cumulative update: stability before flashy additions.

Security Patches Hidden Until June Patch Tuesday

Microsoft’s policy is to withhold detailed security disclosures for preview updates. KB5089570 contains the same security fixes slated for June 2026’s Patch Tuesday, but the company won’t enumerate CVEs until then. This prevents attackers from reverse-engineering the patches before the vast majority of users are protected.

Historically, preview updates pack a mix of critical, important, and moderate vulnerabilities. Given recent campaigns targeting Windows kernel escalation flaws and remote desktop services, IT teams should assume at least a few high-severity patches are bundled. The update does not introduce any known functional changes to security features like Windows Defender, but it likely patches bugs in how the kernel handles certain objects or how networking components validate input.

One subtle but important change: Secure Boot DBX revocations appear to be included. Microsoft periodically updates the list of vulnerable boot modules to block outdated firmware signatures. This helps defend against rootkits like BlackLotus that exploit old boot managers. The dbx list update might be flagged separately in the final Patch Tuesday notes.

Other Notable Fixes and Known Issues

Beyond File Explorer, users report a few additional improvements. The taskbar search box now respects the system accent color more reliably when using custom color modes. An issue where Alt+Tab would occasionally show stale thumbnails has also been corrected.

For enterprise administrators, Group Policy processing order has been tweaked. A rare race condition during startup could delay the application of folder redirection policies; KB5089570 addresses that timing problem. Virtual Print Queue installations no longer stall when deploying via Configuration Manager.

No piece of software is bug-free, and this preview does carry some known issues. The Windows Update settings page might incorrectly report “Some settings are managed by your organization” on personal devices that aren’t domain-joined. Microsoft is investigating and says it’s a reporting error, not a policy conflict.

Another hiccup: users of the Dev Home app might see a blank dashboard after applying this update. A subsequent Dev Home update from the Microsoft Store resolves the glitch. If you rely on Dev Home for development workflows, plan to update that app separately.

Should You Install KB5089570 Now?

For most home users, the answer is a cautious “no.” Preview updates are optional precisely because they haven’t undergone the full rollout validation that Patch Tuesday updates get. Unless you’re experiencing a specific issue that KB5089570 is known to fix—like the File Explorer address bar hang—it’s safer to wait for the mandatory June 2026 cumulative update. You’ll still get these improvements in a couple of weeks, along with any last-minute fixes for issues discovered during this preview phase.

IT administrators, on the other hand, should jump on this update in a test ring. Deploy it to a representative set of machines in your organization and validate line-of-business applications. Pay special attention to file-sharing workflows, VPN client compatibility, and custom Explorer extensions. If nothing breaks, you’ll have a head start on Patch Tuesday with confidence that your fleet won’t face regression.

Power users and enthusiasts who like living on the edge can grab the update manually from the Microsoft Update Catalog. Apply it, kick the tires on the File Explorer fixes, and report any new issues via the Feedback Hub. That feedback loop helps Microsoft refine the update before it becomes mandatory.

Community Chatter and Early Reactions

Over on the Windows enthusiast forums, early adopters are cautiously optimistic. Several IT pros report that the update installed without incident on Dell, HP, and Lenovo laptops running standard configurations. A few users with custom RAID arrays saw no boot failures. The most common praise centers on the noticeably snappier File Explorer navigation, especially when jumping between network shares and local drives.

A minority of users report that the taskbar animation stutters after installation, but subsequent reboots often clear the problem. One user noted that the update enabled Credential Guard on a machine that had previously turned it off via BIOS—likely a side effect of the Secure Boot DBX update touching firmware settings. If you’ve deliberately disabled security mitigations, double-check your BIOS after installing.

Microsoft’s own support article for KB5089570 is, at the time of writing, bare-bones. The company promises to flesh out the notes once the update ships in June. Until then, the community-driven changelog collected on forums serves as the best source of what’s actually changed.

How to Get the Update

If you decide to install KB5089570, here are your options:

  • Windows Update: Go to Settings > Windows Update, enable “Get the latest updates as soon as they’re available,” and check for updates. The preview will appear as an optional download.
  • Microsoft Update Catalog: Search for KB5089570 on the Catalog website, download the MSU file matching your system architecture (x64 or ARM64), and run it manually.
  • Windows Update for Business: Configure your deployment rings to allow preview builds; the update will offer itself according to your policies.

After installation, your system will reboot and report build 28000.2179 in System > About or via the winver command.

The Road Ahead for 26H1

KB5089570 is one of the first preview updates for the 26H1 platform, and it sets expectations for how Microsoft will service this release. The focus on File Explorer performance suggests the company is listening to longstanding complaints. With Windows 11’s UI still a work in progress after several feature updates, each cumulative patch chips away at the rough edges.

Looking forward, the next milestone for 26H1 will be the June 2026 Patch Tuesday rollout. That update will make all these fixes widely available and add whatever new security protections Redmond deems necessary. Later in the year, version 26H2 is rumored to enter the Canary Channel, possibly bringing more radical changes to the desktop experience.

For now, KB5089570 is a modest but meaningful step toward a more polished Windows 11. If you’re responsible for managing Windows devices, carve out time this week to test it. The smoother your fleet runs after Patch Tuesday, the less firefighting you’ll do next month.