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Claude Code Issues / #27397

[BUG] Cowork regression: worked on v1.1.3770, broken on v1.1.3918 — yukonSilver incorrectly marks win32/x64 as unsupported (Windows 11 Home)

Status Fixed / completed
Maintainer reply None cached
Workaround ✓ Mentioned in description ↑
Activity 5 comments · opened Feb 21, 2026 · closed Feb 22, 2026

Preflight Checklist

  • [x] I have searched existing issues and this hasn't been reported yet
  • [x] This is a single bug report (please file separate reports for different bugs)
  • [x] I am using the latest version of Claude Code

What's Wrong?

<html>
<body>
<!--StartFragment--><html><head></head><body><h2>Preflight Checklist</h2>
<ul>
<li>[x] I have searched existing issues and this hasn't been reported yet</li>
<li>[x] This is a single bug report</li>
<li>[x] I am using the latest version of Claude Code</li>
</ul>
<h2>What's Wrong?</h2>
<p>Cowork was working perfectly on v1.1.3770.0 but broke after auto-update to v1.1.3918.0. The <code>yukonSilver</code> platform detection now marks the system as <code>unsupported (win32/x64)</code> despite the VM having run successfully minutes earlier on the same hardware.</p>
<h3>Timeline (2026-02-21)</h3>
<ul>
<li><strong>11:33</strong> — App starts, detects rootfs.vhdx version mismatch, promotes new bundle from warm cache</li>
<li><strong>11:34:39</strong> — <code>smol-bin.x64.vhdx</code> copied from <strong>v1.1.3770.0</strong> path → VM starts successfully</li>
<li><strong>11:34:49</strong> — Network: CONNECTED, API reachability: REACHABLE</li>
<li><strong>11:34:52</strong> — SDK installed, startup complete (96248ms)</li>
<li><strong>11:36–11:45</strong> — Multiple Cowork sessions spawned and completed successfully</li>
<li><strong>11:45:32</strong> — Last successful process exits cleanly</li>
<li><strong>(PC restarted for unrelated WiFi issue)</strong></li>
<li><strong>11:54:58</strong> — <code>yukonSilver not supported (status=unsupported)</code> — deletes VM bundle reinstall files</li>
<li><strong>11:55:12+</strong> — Repeated <code>[startVM] VM not supported (win32/x64), skipping</code></li>
</ul>
<h3>Key Evidence: Version Mismatch Caused the Regression</h3>
<p>During the <strong>working</strong> session, the log shows:</p>
<pre><code>[VM:start] Copying smol-bin.x64.vhdx to bundle: C:\Program Files\WindowsApps\Claude_1.1.3770.0_x64__pzs8sxrjxfjjc\app\resources\smol-bin.x64.vhdx
</code></pre>
<p>After restart, the installed version is <strong>1.1.3918.0</strong> — the old 3770 package was removed. The new version's <code>yukonSilver</code> platform check incorrectly classifies this system as unsupported.</p>
<h3>Environment</h3>

Component | Value
-- | --
Claude Desktop | v1.1.3918.0 (Microsoft Store / MSIX)
Previous working version | v1.1.3770.0
OS | Windows 11 Home 23H2 (Build 22631.6199)
CPU | Intel Core i7-14650HX 2.20 GHz
RAM | 32 GB
Device | Lenovo Legion 5 (PN: 83DG003SSC, BIOS: NMCN32WW)
Hyper-V | Enabled via DISM workaround (Windows Home)
CoworkVMService | Running, StartType: Automatic
Hypervisor | Detected (systeminfo confirms)
Virtual Machine Platform | ✅ Enabled
Windows Hypervisor Platform | ✅ Enabled

<h3>Diagnostic Commands</h3>
<pre><code class="language-powershell">PS&gt; systeminfo | findstr "Hyper-V"
Hyper-V Requirements: A hypervisor has been detected. Features required for Hyper-V will not be displayed.

PS&gt; Get-Service CoworkVMService | Select-Object Name, Status, StartType
Name Status StartType
---- ------ ---------
CoworkVMService Running Automatic

PS&gt; sc.exe qc CoworkVMService
BINARY_PATH_NAME: "C:\Program Files\WindowsApps\Claude_1.1.3918.0_x64__pzs8sxrjxfjjc\app\resources\cowork-svc.exe"

PS&gt; Get-AppxPackage Claude | Select-Object Name, Version
Name Version
---- -------
Claude 1.1.3918.0
</code></pre>
<h3>Relevant Log Excerpts</h3>
<p><strong>Working session (v1.1.3770 code path):</strong></p>
<pre><code>2026-02-21 11:34:39 [info] [VM:start] Copying smol-bin.x64.vhdx to bundle: C:\Program Files\WindowsApps\Claude_1.1.3770.0_x64__pzs8sxrjxfjjc\app\resources\smol-bin.x64.vhdx
2026-02-21 11:34:40 [info] [VM:start] Windows VM service configured
2026-02-21 11:34:49 [info] [VM] Network status: CONNECTED
2026-02-21 11:34:49 [info] [VM] API reachability: REACHABLE
2026-02-21 11:34:52 [info] [VM:start] Startup complete, total time: 96248ms
</code></pre>
<p><strong>After restart (v1.1.3918 code path):</strong></p>
<pre><code>2026-02-21 11:54:58 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
2026-02-21 11:54:58 [info] [deleteVMBundle] Deleting reinstall files from C:\Users\[user]\AppData\Roaming\Claude\vm_bundles\claudevm.bundle
2026-02-21 11:55:12 [warn] [startVM] VM not supported (win32/x64), skipping
</code></pre>
<p><strong>Historical pattern</strong> — <code>yukonSilver not supported</code> has appeared since Jan 23 / Feb 6, but Cowork <strong>bypassed this check and worked anyway</strong> until the 3770→3918 update removed the old code path.</p>
<h3>Steps to Reproduce</h3>
<ol>
<li>Have a working Cowork setup on Windows 11 Home with Hyper-V enabled via DISM</li>
<li>Allow Claude Desktop to auto-update from v1.1.3770.0 to v1.1.3918.0</li>
<li>Restart PC</li>
<li>Open Claude Desktop → Cowork tab</li>
<li>Observe: "Virtualization is not enabled" error, logs show <code>VM not supported (win32/x64)</code></li>
</ol>
<h3>Expected Behavior</h3>
<p>Cowork should start successfully on Windows 11 Home with Hyper-V enabled via DISM, as it did on v1.1.3770.0.</p>
<h3>Actual Behavior</h3>
<p><code>yukonSilver</code> platform detection in v1.1.3918.0 classifies win32/x64 with DISM-enabled Hyper-V as "unsupported". The VM never attempts to start.</p>
<h3>Related Issues</h3>
<ul>
<li>#25136 — yukonSilver marked as unsupported on Windows 11 Pro x64</li>
<li>#24918 — Windows 11 Home: Cannot connect to Claude API</li>
<li>#25241 — Windows 11 Home: VM boots but API unreachable</li>
<li>#26090 — Windows 10 Home: Cowork tab not showing</li>
</ul></body></html><!--EndFragment-->
</body>
</html>

What Should Happen?

Cowork should start successfully on Windows 11 Home with Hyper-V enabled via DISM, as it did on v1.1.3770.0. The VM should boot, connect to the network, reach the Claude API, and allow task execution.

Error Messages/Logs

Steps to Reproduce

  1. Have a working Cowork setup on Windows 11 Home with Hyper-V enabled via DISM
  2. Allow Claude Desktop to auto-update from v1.1.3770.0 to v1.1.3918.0
  3. Restart PC
  4. Open Claude Desktop → Cowork tab
  5. Observe: "Virtualization is not enabled" error, logs show VM not supported (win32/x64)

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

1.1.3770.0

Claude Code Version

1.1.3918.0

Platform

Other

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_

View original on GitHub ↗

5 Comments

github-actions[bot] · 6 months ago

Found 3 possible duplicate issues:

  1. https://github.com/anthropics/claude-code/issues/27323
  2. https://github.com/anthropics/claude-code/issues/27354
  3. https://github.com/anthropics/claude-code/issues/27340

This issue will be automatically closed as a duplicate in 3 days.

  • If your issue is a duplicate, please close it and 👍 the existing issue instead
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🤖 Generated with Claude Code

Alex-Saad · 6 months ago

I have this issue can you investigate if it is indeed a bug or there is anything I can do?

Environment:

OS: Windows 11 Pro 25H2 (Build 26200.7462) — received via standard Windows Update, not Insider Programme
Hardware: Dell Latitude 7400 (physical machine, confirmed not a VM)
Installer: Claude Setup.exe (direct download from claude.ai/download)
Windows Features enabled:
Microsoft-Hyper-V-All ✅
HypervisorPlatform ✅
VirtualMachinePlatform ✅
WSL2 installed with Ubuntu ✅
Services running:
vmms (Running, Automatic)
vmcompute (Running, Manual)
hns (Running, Manual)
Relevant log output from cowork_vm_node.log:
2026-02-21 10:21:44 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle... 2026-02-21 10:22:37 [warn] [startVM] VM not supported (win32/x64), skipping
Error shown in UI:
"Virtualization is not enabled. Claude's workspace requires hardware virtualization (Hyper-V). Enable virtualization in your computer's BIOS/UEFI settings, then restart."
This error is misleading — hardware virtualization is confirmed enabled and all required features are active. The issue appears to be yukonSilver incorrectly flagging this win32/x64 environment as unsupported despite full Hyper-V support being present.

adamlovesai · 6 months ago

Same issue here. Windows 11 Pro 25H2 (Build 26200.7840), i7-8700K,
Claude Desktop 1.1.3918 (a4b368). Cowork was working earlier today,
broke after silent auto-update. Hyper-V fully enabled and running.
Logs show identical yukonSilver unsupported / VM not supported (win32/x64).

MarshallOfSound · 6 months ago

Closing as duplicate of #27316 which was very rapidly fixed in the v1.1.3963 release

github-actions[bot] · 6 months ago

This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.

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