[BUG] Claude Desktop MSIX installation fails with HRESULT 0x80073CFF on Windows 11 Pro — AddPackage error persists across all configurations

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?

The Claude Desktop installer consistently fails at the MSIX AddPackage step with HRESULT 0x80073CFF. I have exhausted every troubleshooting option available to me — the error persists across all configurations.
Troubleshooting attempted (all failed):

Originally on Windows 11 Home ("Core") — failed
Purchased and upgraded to Windows 11 Pro ("Professional") — still fails
Enabled Hyper-V and rebooted — still fails
Enabled "Allow all trusted apps to install" in Group Policy — still fails
Sideloading is enabled, S Mode is off
Installer runs as administrator (elevated context confirmed in log)
Tried multiple installer versions across 5+ attempts over two sessions (May 12 and May 18, 2026)

System info:

Windows edition: Professional
Windows version: 10.0.26200
Architecture: x64
DPI: 96 (100%)
Installer versions: 2dbd7802ab (May 12) and abcd6556f7 (May 18)

What Should Happen?

The Claude Desktop installer should successfully complete the MSIX AddPackage installation on Windows 11 Pro (build 10.0.26200) with Hyper-V enabled and sideloading enabled. If the full install with Cowork fails, the installer should provide a working fallback option to install without Cowork — currently the error dialog mentions this option but the installer closes without offering it.

Error Messages/Logs

2026/05/18 12:20:35.523695 Installing via AddPackage (current-user)...
2026/05/18 12:20:36.032225 MSIX installation failed: AddPackage failed: AddPackage failed with HRESULT 0x80073CFF
2026/05/18 12:20:36.032225 ERROR dialog (opening log): Installation failed: AddPackage failed: AddPackage failed with HRESULT 0x80073CFF

The MSIX signature verifies successfully every time (WinVerifyTrust: MSIX signature is valid, Signature verified: MSIX signer matches bootstrapper). The failure occurs immediately at the AddPackage call.
Expected behavior:
Claude Desktop should install successfully with Cowork on Windows 11 Pro with Hyper-V enabled.
Full setup log attached — covers all attempts from both sessions.

Steps to Reproduce

1. Download Claude Desktop installer from claude.com/download on a fresh Windows 11 Pro system (no previous Claude installation)
2. Run "Claude Setup.exe"
3. Accept the UAC elevation prompt when asked
4. Installer downloads the MSIX package successfully and signature verifies
5. Installation fails at AddPackage with HRESULT 0x80073CFF
6. Error dialog says "You can try again or install without Cowork" but provides no clickable option to install without Cowork — the installer simply closes
7. Issue persists across multiple attempts and after enabling Hyper-V, enabling sideloading, and configuring Group Policy to allow all trusted apps
8. Get-AppxPackage Claude returns nothing — no previous or ghost packages on the system

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

N/A

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Note: This is a Claude Desktop app installer bug, not a Claude Code issue. Filing here as there is no separate Desktop app issue tracker. See #49917 for a potentially related MSIX AddPackage failure (different error code, 0x80073CF6, but similar symptoms).

ClaudeSetup.log