Windows 11’s September Patch Tuesday brings a sizeable, feature-packed cumulative update—KB5065426 (Build
26100.6584)—that mixes small but welcome taskbar and File Explorer polish with deeper on-device AI components and an unusually large offline payload that deserves careful attention from both home users and IT teams.
Background / Overview
Microsoft released KB5065426 as part of the September 9, 2025 Patch Tuesday cycle. The update advances Windows 11 24H2 machines to
Build 26100.6584 and is being offered through Windows Update and the Microsoft Update Catalog as an
.msu offline installer for administrators and users who prefer manual deployment. Microsoft’s combined servicing approach for Windows 11 (checkpoint cumulative updates) means the cataloged packages may include both SSU and LCU payloads; installing via the Update Catalog remains the recommended manual path. Two facts stand out immediately:
- The update surfaced visible UI changes (taskbar/calendar, permission prompts) and small app-UX improvements (Click to Do tutorial, File Explorer tweaks).
- The offline
.msu packages are very large—multiple gigabytes—because Microsoft’s on-device generative AI models for Copilot features are included in the payloads shipped to all architectures. That decision has meaningful implications for bandwidth, disk space, and deployment workflows.
This article unpacks the update, verifies core technical points, analyses the benefits and risks, and offers practical guidance for users and IT administrators planning deployment.
What KB5065426 delivers: feature roundup
Headline items
- Taskbar / Calendar flyout: A full clock view returns to the calendar flyout (similar in function to Windows 10’s full clock), bringing back a larger time display when you open the date/time calendar. This restores a long-requested convenience for users who relied on the expanded flyout clock.
- Recall (Copilot+ devices): The Recall experience gains a new homepage that aggregates recent snapshots, top apps, and recent websites—aimed at faster task resumption on NPU-equipped Copilot+ PCs. Recall remains opt-in and tied to hardware with on-device NPUs.
- Click to Do tutorial: Click to Do now includes an interactive, re-launchable tutorial to improve discoverability of text-and-image assistant actions.
- System permission prompts: Microsoft changed how some hardware permission prompts are presented—displaying a dimmed, focused full-screen prompt in certain scenarios to make consent dialogs more prominent.
- File Explorer UI and AI actions: Explorer receives visual polish and context-menu AI actions (image edits and searches) that surface common workflows inline. These actions are being staged and gated by hardware and licensing (Copilot/Microsoft 365 entitlements in some cases).
Download sizes and payload composition
Direct
.msu download entries posted in the Microsoft Update Catalog report very large downloads:
- ARM64: approximately 3,685.4 MB
- x64 (client): approximately 3,811.1 MB
- x64 (Server 24H2): approximately 3,811.1 MB
Those sizes are strikingly large for a single monthly cumulative update and are comparable to small Windows ISO images. Microsoft has shipped on-device AI model binaries in these packages—models that are technically required to power Copilot capabilities on eligible hardware—even though those models are included in the installers for all systems. This is the primary reason for the multi-gigabyte package sizes.
Deep dive: key features and technical verification
1) Recall — new homepage, NPU dependency, and disable options
Recall’s redesign surfaces a “Home” overview of recent activities and snapshot collections for faster resumption. Multiple reports confirm that Recall depends on specialized hardware—machines designated by Microsoft as
Copilot+ with an on-device NPU—and that Recall functionality is opt‑in by design. The update places the UI scaffolding in Build
26100.6584, but server-side gating and hardware checks control full activation. (
windowslatest.com, windowslatest.com, windowslatest.com, windowslatest.com, windowslatest.com,
bleepingcomputer.com)
Practical guidance:
- Verify SSD firmware is on a released production version; avoid pre-release engineering firmware unless directed by vendor documentation.
- Keep backups before installing major cumulative updates.
- If you suspect storage problems after patching, collect logs and contact vendor support—do not continue heavy writes that could exacerbate a failing SSD.
Enterprise considerations: deployment and manageability
- Checkpoint cumulative updates: The Windows 11 servicing model (checkpoint cumulative updates) means offline installers may include SSU and LCU components. When deploying manually, administrators should confirm prerequisites for offline images and follow Microsoft guidance for ordering MSU application where necessary. The Microsoft guidance emphasizes using the Update Catalog and DISM or WUSA appropriately. (support.microsoft.com)
- Bandwidth and caching: Expect multi-gigabyte payloads on distribution points. Plan for network scheduling and peer caching (Delivery Optimization) where possible to reduce peak bandwidth usage.
- Feature gating and variability: Many of the AI-facing features are gated server-side or by entitlement/hardware (Copilot+). That increases the diversity of experience across a managed fleet on the same build number. Pilot testing and targeted telemetry collection remain essential before broad rollouts.
- Privacy and compliance: New features that capture snapshots or surface recent activity (Recall) raise compliance questions in regulated environments. Evaluate whether to allow those features on corporate devices, configure group policies or MDM controls, and update privacy notices. Microsoft and community reporting stress that Recall is optional and should be controllable at the IT policy level, but teams must validate controls in their environment. (windowslatest.com, windowslatest.com, tomshardware.com, tomshardware.com, answers.microsoft.com, windowslatest.com)
- Document any differences users may see after updating (e.g., new permission prompt behavior, taskbar clock display) so helpdesk scripts can quickly triage UI questions versus true regressions.
Final analysis: balancing polish, AI, and manageability
KB5065426 is emblematic of Microsoft’s current Windows strategy: fuse incremental UX restorations (taskbar clock, calendar flyout) with early-stage on-device AI capabilities that promise real productivity improvements. For users who benefit from the AI features and own Copilot+ hardware, the changes present tangible shortcuts. For IT administrators, however, the update magnifies operational complexity—gigabyte-scale offline installers, firmware dependencies, and feature-gating that fragments end-user experiences across identical builds.
The trade-offs are clear:
- Users gain convenience and new AI-driven workflows.
- Administrators and bandwidth-constrained users incur larger downloads and must add firmware checks to pre-deployment testing.
The prudent path is cautious, measured adoption: pilot widely, update firmware proactively, and rely on Windows Update for most consumer devices while using the Microsoft Update Catalog for targeted offline installs when required. Backups and a firm understanding of which machines qualify as Copilot+ will reduce surprises.
KB5065426 is not an emergency for most users, but it is one of those updates that deserves attention for its operational implications. The return of small, appreciated UI features—combined with the front-loading of AI model payloads—marks another step in Windows 11’s evolution toward blended UI/AI experiences. Whether that evolution is worth the bandwidth and management cost will depend on each organization’s priorities and tolerance for heterogeneity in feature exposure. (
windowslatest.com, Windows 11 KB5065426 24H2 out with taskbar features, direct download links (.msu)