Microsoft has finally closed out a five-week bug that stopped Teams and the new Outlook from opening on ARM-based Windows PCs, and the fix landed quietly in this week's Patch Tuesday. The company confirmed the resolution today, September 11, after weeks of pointing affected users toward an unrelated AI graphics package as a stopgap.

The trouble started with the August 11 security update. Afterward, Teams and the redesigned Outlook for Windows would fail to launch, or would open and then close on their own, but only on Arm64 machines: Surface Laptop 7, Surface Pro 11, and other Snapdragon X-based Copilot+ PCs running Windows 11 24H2 or later. Classic Outlook kept working. So did Word, Excel, and everything else. The break was narrow, and it happened to land on exactly the two apps Microsoft has spent the last two years positioning as its proof that Windows on ARM is ready for real work.

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What actually broke, and on which machines?

Two updates triggered it, split by Windows version: KB5121003 for 24H2 and 25H2, KB5121000 for the newer 26H1 branch, both released August 11. Microsoft did not flag the problem publicly right away. It posted an advisory to the Windows release health dashboard on September 1 at 7:20 PM Pacific, three weeks after the update shipped, once enough Arm64 users had reported broken launches for a pattern to be obvious. The workaround Microsoft offered at that point was strange on its face: update the Auto Super Resolution package to version 1.0.19.0 or later through the Microsoft Store. ASR is a Copilot+ feature that uses on-device AI to upscale game graphics. It has nothing to do with productivity apps. Microsoft never explained why updating it stopped Teams and Outlook from crashing, only that it did.

From broken launch to permanent fix, five weeks on ARM Windows An August 11 security update broke Teams and Outlook launches on Arm64 Windows PCs. Microsoft offered a workaround via an Auto Super Resolution update on September 1, then shipped a permanent fix on September 8 that was confirmed working by September 11. WINDOWS 11 ON ARM · SNAPDRAGON X / COPILOT+ PCS ONLY KB5121003Aug 11 update Teams + Outlookfail to launch ASR 1.0.19.0workaround, Sept 1 KB5124008 / 5124012permanent fix Aug 11, 2026Aug 11 – Sept 1Sept 1, 2026Sept 8 – 11, 2026 An AI upscaling package patched an app-launch bug, unexplained, for five weeks genztech.blog
Fig 1 A security update broke launches on Arm64 Windows only. The first relief came from an unrelated AI graphics package; the real fix shipped in this week's Patch Tuesday and was confirmed working today.

Why would an AI upscaling tool fix an app-launch bug?

New Outlook and modern Teams are both built on WebView2, the Edge-based runtime Microsoft uses to wrap web apps as desktop clients. That runtime shares low-level rendering and graphics-driver plumbing with other Windows components, and Auto Super Resolution sits right in that same graphics stack on Copilot+ hardware. A change tucked inside an ASR update touching that shared plumbing is a plausible explanation for why updating a game-upscaling package would stop two unrelated apps from crashing. It is a plausible explanation, not a confirmed one. Microsoft's own advisory never said why the workaround worked, and it still has not, even in this week's fix notes.

How many people did this actually hit?

Microsoft does not publish ARM's share of the active Windows install base, so there is no clean number to cite here. What is verifiable is the trend: Arm64 PCs were a rounding error before Copilot+ launched in 2025, and Qualcomm's Snapdragon X chips plus Microsoft's own Surface Pro 11 and Surface Laptop 7 have been the spearhead of Microsoft's push to make Windows on ARM a real alternative to x86 laptops, not a compatibility-mode curiosity. That push depends on flagship Microsoft apps working at least as well on ARM as on Intel or AMD silicon. A month where the company's own collaboration suite and mail client didn't reliably open on its own reference hardware undercuts exactly the pitch it's making to developers and IT buyers.

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What was the actual timeline?

  1. Aug 11, 2026KB5121003 / KB5121000 ship. Routine August security updates for Windows 11 24H2/25H2 and 26H1.
  2. Late Aug 2026Reports of Teams and Outlook crashes surface. Limited to Arm64 devices; classic Outlook and other apps unaffected.
  3. Sept 1, 2026Microsoft posts a release-health advisory at 7:20 PM PT. Confirms the issue, ties it to the August update, offers the ASR workaround.
  4. Sept 8, 2026September Patch Tuesday ships KB5124008 and KB5124012. Each KB's own release notes state the Teams/Outlook Arm64 fix explicitly.
  5. Sept 9–11, 2026Fix confirmed, coverage catches up. Microsoft marks the release-health entry resolved; the workaround is no longer necessary for anyone on the new builds.

What should ARM Windows users do now?

Nothing manual is required going forward. Installing the regular September cumulative update, KB5124008 on 24H2/25H2 or KB5124012 on 26H1, through Windows Update carries the fix. Anyone who already applied the Auto Super Resolution workaround does not need to undo it; it can stay installed. If Teams or new Outlook is still crashing after the September update is confirmed installed, that points to a separate problem, not this one, and is worth its own support ticket rather than another round of the ASR fix.

What to watch
  • Whether Microsoft ever explains the ASR connection. A root cause has not been published. If it never is, this becomes a case study in shipping a fix without disclosing the mechanism.
  • Patch Tuesday QA on Arm64 specifically. This is not the first time an update has behaved differently on ARM than on x86; watch whether Microsoft adds Arm64-specific regression testing to its release process or whether this repeats.
  • Copilot+ PC momentum through the rest of 2026. Microsoft needs enterprise IT to trust ARM procurement. A five-week outage in its own flagship apps is the kind of story that shows up in vendor risk assessments.

Our take

Credit where it's due: Microsoft posted a public advisory once the pattern was clear, named the exact builds, and shipped a real fix inside a month, which beats staying silent or burying it in a forum thread. But the transparency stopped at "here's what to install." The company never said why an AI upscaling package fixed a productivity-app crash, and that gap matters more here than it would on a cosmetic bug, because these are the two apps Microsoft is using to argue that Windows on ARM is a first-class platform. Selling Snapdragon X laptops on parity with Intel and AMD machines is a harder pitch when the parity story includes a month where the pitch's own headline apps didn't reliably open.

Primary sources

Original analysis by GenZTech, based on Microsoft's own KB release notes. Figures current as of September 11, 2026.