[BUG] Claude Desktop installation fails with HRESULT 0x80073CFF on Windows 11 Pro 10.0.26200 (fully updated)

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?

Claude Desktop installation fails with HRESULT 0x80073CFF on Windows 11 Pro 10.0.26200 despite sideloading enabled, Developer Mode registry set, and Group Policy configured. Package origin classified as "Unknown" by Windows AppX deployment engine. Signature from CN="Anthropic, PBC" validates correctly but installation still rejected. Persists after all documented workarounds including manual Add-AppxPackage via PowerShell.

What Should Happen?

Claude Desktop should install successfully on Windows 11 Pro with administrator privileges, sideloading enabled, and AllowDevelopmentWithoutDevLicense set to 1. The MSIX package signed by Anthropic should be accepted by the Windows AppX deployment engine without requiring additional enterprise licensing or domain configuration.

Error Messages/Logs

AllowDevelopmentWithoutDevLicense found with value: 1
Windows edition: Professional
Windows version: 10.0.26200
Native arch: x64
Elevation type: Full
Is elevated: true
Sideloading enabled: true
S Mode: false
Conflicting service: false
Installing via AddPackage (current-user)...
MSIX installation failed: AddPackage failed: AddPackage failed with HRESULT 0x80073CFF

Event Log (Get-AppPackageLog):
ID 413: Deployment of package Claude_1.11187.4.0_x64__pzs8sxrjxfjjc with package origin Unknown failed because no valid license or sideloading policy could be applied.
ID 157: The app package signature was validated for core content published by CN="Anthropic, PBC", O="Anthropic, PBC", L=San Francisco, S=California, C=US
ID 605: Error 0x80073CFF: Failure in the Approved state handler.

Workarounds attempted (all failed):
- Run installer as administrator
- Set HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock\AllowDevelopmentWithoutDevLicense = 1
- Set HKLM\SOFTWARE\Policies\Microsoft\Windows\Appx\AllowAllTrustedApps = 1
- gpupdate /force + reboot
- Installed Anthropic certificate manually to TrustedPeople store
- Add-AppxPackage directly via PowerShell with -ForceApplicationShutdown and -AllowUnsigned flags
- Windows fully updated (KB5089549 installed, build 26200.8457)

Steps to Reproduce

1. Download Claude Desktop installer from claude.ai/download (Windows x64)
2. Right-click installer → "Run as administrator"
3. Observe HRESULT 0x80073CFF error

If attempting manual workarounds:

1. Open PowerShell as administrator
2. Run: reg add "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock" /t REG_DWORD /f /v "AllowDevelopmentWithoutDevLicense" /d "1"
3. Run: reg add "HKLM\SOFTWARE\Policies\Microsoft\Windows\Appx" /t REG_DWORD /f /v "AllowAllTrustedApps" /d "1"
4. Run: gpupdate /force
5. Reboot
6. Run installer again as administrator → same error
7. Run: Add-AppxPackage -Path "Claude.msix" → same error
8. Run: Get-AppPackageLog to confirm "package origin Unknown" as root cause

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

N/A - Claude Desktop installer bug

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Terminal.app (macOS)

Additional Information

This is a Claude Desktop installer bug, not a Claude Code bug.
Reporting here because no dedicated installer issue tracker exists.

The root cause appears to be that Windows AppX deployment engine
classifies the MSIX package origin as "Unknown" despite valid
Anthropic signature, blocking installation regardless of sideloading
policy. This affects Windows 11 Pro build 26200.8457 (fully updated
as of June 2026).

Related closed issue: #53634 (closed as not planned, same error,
different build — that issue was not resolved, only dismissed).