[BUG] Cowork regression: worked on v1.1.3770, broken on v1.1.3918 — yukonSilver incorrectly marks win32/x64 as unsupported (Windows 11 Home)
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?
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<!--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> systeminfo | findstr "Hyper-V"
Hyper-V Requirements: A hypervisor has been detected. Features required for Hyper-V will not be displayed.
PS> Get-Service CoworkVMService | Select-Object Name, Status, StartType
Name Status StartType
---- ------ ---------
CoworkVMService Running Automatic
PS> sc.exe qc CoworkVMService
BINARY_PATH_NAME: "C:\Program Files\WindowsApps\Claude_1.1.3918.0_x64__pzs8sxrjxfjjc\app\resources\cowork-svc.exe"
PS> 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>
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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
- Have a working Cowork setup on Windows 11 Home with Hyper-V enabled via DISM
- Allow Claude Desktop to auto-update from v1.1.3770.0 to v1.1.3918.0
- Restart PC
- Open Claude Desktop → Cowork tab
- 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_
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