Cowork "Virtualization is not available" — HRESULT 0x80370102 despite functional Hyper-V (New-VM works, HCS processortopology returns catastrophic error)

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?

Cowork shows "Virtualization is not available — Claude's workspace requires Virtual Machine Platform, but the virtualization service isn't responding." The VM never initializes.

Key finding: New-VM -Name "test-vm" -MemoryStartupBytes 512MB -Generation 2 works perfectly (Hyper-V is fully functional), but hcsdiag hostproperties processortopology returns "Catastrophic error", causing HCS to fail when Cowork tries to create its lightweight VM.

Environment: Windows 11 Pro 25H2 (Build 26200.8246), Intel i9-14900KS (8 P-cores/16 E-cores hybrid), ASRock Z790M-ITX WiFi (BIOS 19.01 latest), 32GB DDR5, Claude Desktop v1.2773.0.0 (MSIX).

Verification table:

• Task Manager Virtualization: Enabled
• New-VM: Works perfectly
• hcsdiag hostproperties processortopology: CATASTROPHIC ERROR
• hcsdiag hostproperties cpugroup: Works
• CoworkVMService: Running
• vmcompute: Running
• VBS: Running (status=2)
• All Hyper-V features: Enabled
• VT-x, VT-d, SR-IOV: Enabled in BIOS

What Should Happen?

Cowork should detect that Hyper-V is operational and start the VM workspace successfully.

Error Messages/Logs

[info] [VM:start] Configuring Windows VM service...
[info] [VM:start] Windows VM service configured
[info] [VM:steps] create_network completed (1ms)
[info] [VM:steps] create_vm_config started
[error] [VM:start] VM boot failed: HCS operation failed: failed to create compute system: HcsWaitForOperationResult failed with HRESULT 0x80370102: {"Error":-2143878910,"ErrorMessage":"The virtual machine could not be started because a required feature is not installed.","ErrorEvents":[{"Message":"Cannot create system 'cowork-vm-88c28d64' since Hyper-V is not installed on the host."}]}
[error] [VM:start] HCS error detected, available=true, missing=[], sentinel=HYPERVISOR_SERVICE_ERROR

Steps to Reproduce

1. Install Claude Desktop v1.2773.0.0 on Windows 11 Pro 25H2 with Intel i9-14900KS
2. Enable all virtualization features (Hyper-V, VMP, WHP, WSL, Containers)
3. Open Claude Desktop → Cowork tab
4. Error appears immediately. VM never initializes.
5. Run: New-VM -Name "test" -MemoryStartupBytes 512MB -Generation 2 → WORKS
6. Run: hcsdiag hostproperties processortopology → "Catastrophic error"

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

1.2773.0.0 (Claude Desktop, not Claude Code CLI)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Everything attempted (nothing worked):

• Enabled/disabled/re-enabled all Hyper-V features via DISM
• Repair install Windows 10, then full upgrade to Windows 11 Pro 25H2
• Updated BIOS from 11.10 to 19.01 (latest)
• bcdedit: hypervisorlaunchtype auto, nx AlwaysOn, vsmlaunchtype auto
• DISM RestoreHealth + sfc /scannow (found and repaired corrupted files)
• Reinstalled Containers feature
• Cleaned HNS state registry
• Deleted vm_bundles and claude-code-vm (both APPDATA and MSIX paths)
• Uninstalled NordVPN, Valorant/Vanguard, disabled Radmin VPN
• Toggled VT-x off/on in BIOS, enabled VT-d, SR-IOV
• All Windows Updates installed

Root cause: HCS cannot read processor topology on i9-14900KS hybrid P-core/E-core architecture. hcsdiag hostproperties processortopology consistently returns "Catastrophic error" while cpugroup works fine. Standard Hyper-V (New-VM) works perfectly, confirming the hypervisor is operational. The issue is specific to HCS.

Related: #27316, #27317, #29887, #30997, #32004, #33784, #34201, #42227, #45715