[BUG]

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?

اكتب زي كذا:

The Claude Desktop installer consistently fails at the MSIX AddPackage step with HRESULT 0x80073CFF on Windows 11 Professional (build 10.0.26200). This has now failed identically across at least 4 separate installation attempts on the same machine.

The installer runs as a standard user, self-elevates via UAC successfully (confirmed Administrator role via PowerShell: IsInRole(Administrator) = True), the MSIX signature verifies correctly (WinVerifyTrust: MSIX signature is valid), and no existing/conflicting Claude packages are found. Despite full administrator privileges and a clean system, AddPackage fails within ~1-2 seconds every time with HRESULT 0x80073CFF.

Troubleshooting already attempted without success:
- DISM /Online /Cleanup-Image /RestoreHealth — completed successfully, no corruption found
- sfc /scannow — completed successfully, no integrity violations found
- Re-registering all AppX packages via Add-AppxPackage -Register (run as Administrator, confirmed elevated) — completed without resolving the issue
- Full system restart after each attempt

The error dialog states "Administrator access is required to install Claude with full features" — but this is misleading, since the log confirms full elevation was achieved and the actual failure occurs at the AddPackage registration step itself, not due to missing admin rights.

Full setup logs attached (ClaudeSetup.log, multiple attempts) showing identical failure signature every time.

What Should Happen?

Claude Desktop should install successfully via MSIX/AddPackage on Windows 11 Professional (build 10.0.26200) when running with full administrator elevation, a valid signature, and no conflicting packages present.

If the MSIX installation path cannot succeed on this system configuration, the installer should reliably fall back to the "install without Cowork" path (Squirrel installer) and complete installation successfully, rather than requiring the user to manually locate and trigger that fallback after repeated AddPackage failures.

Additionally, the error message "Administrator access is required to install Claude with full features" should not be shown when the log already confirms the process is fully elevated (Is elevated: true) — the dialog should instead surface the actual AddPackage failure reason.

Error Messages/Logs

2026/07/15 20:23:18.697881 Elevation type: Full
2026/07/15 20:23:18.697881 Is elevated: true
2026/07/15 20:23:18.697881 Sideloading enabled: true
2026/07/15 20:23:18.697881 Conflicting service: false
2026/07/15 20:23:18.697881 Running in elevated context
2026/07/15 20:23:18.799710 Verifying Authenticode signature on C:\Users\saudi\AppData\Local\Temp\Claude-3536858800.msix
2026/07/15 20:23:20.482142 WinVerifyTrust: MSIX signature is valid
2026/07/15 20:23:21.212148 Signature verified: MSIX signer matches bootstrapper
2026/07/15 20:23:21.220660 Extracted family name from MSIX manifest: Claude_pzs8sxrjxfjjc
2026/07/15 20:23:21.234636 Checking for existing Claude MSIX packages...
2026/07/15 20:23:21.285144 Standard install (not split-account), using AddPackage
2026/07/15 20:23:21.285144 Installing via AddPackage (current-user)...
2026/07/15 20:23:22.325277 MSIX installation failed: AddPackage failed: AddPackage failed with HRESULT 0x80073CFF
2026/07/15 20:23:22.325277 ERROR dialog (opening log): Installation failed: AddPackage failed: AddPackage failed with HRESULT 0x80073CFF

Please share this log with us.

2026/07/15 20:24:02.609698 Elevated process exited with code 1
2026/07/15 20:24:02.609698 Elevation failed: elevated installer exited with code 1
2026/07/15 20:24:02.609698 ERROR dialog (with log path): Administrator access is required to install Claude with full features. You can try again or install without Cowork.

Steps to Reproduce

1. On Windows 11 Professional (build 10.0.26200), download the Claude Desktop installer from claude.com/download.
2. Run "Claude Setup.exe" as a standard (non-elevated) user.
3. The installer detects sideloading is enabled and downloads the MSIX package (~256 MB) automatically.
4. After download completes, the installer self-elevates via a UAC prompt (Claude Setup.exe --elevated --msix-path ... --log-path ...).
5. Accept the UAC prompt.
6. In the elevated process, the MSIX Authenticode signature verifies successfully.
7. The installer checks for existing Claude MSIX packages — none found.
8. The installer attempts to register the package via AddPackage (current-user).
9. AddPackage fails within ~1-2 seconds with: "AddPackage failed: AddPackage failed with HRESULT 0x80073CFF"
10. The elevated process exits with code 1, and the installer shows: "Administrator access is required to install Claude with full features. You can try again or install without Cowork."

Additional troubleshooting performed to rule out system/environment causes (all completed successfully, none resolved the issue):

• DISM /Online /Cleanup-Image /RestoreHealth
• sfc /scannow
• Get-AppXPackage -AllUsers | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"} (run from an elevated PowerShell session, confirmed via IsInRole(Administrator) = True)
• Full system restart after each attempt

Issue reproduces identically across at least 4 separate installation attempts on the same machine. Full setup logs attached.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

N/A — installation has not completed successfully across multiple attempts, so the claude command is not available on this system.

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

Environment:

• OS: Windows 11 Professional, build 10.0.26200
• Architecture: x64
• Windows Update: fully up to date at time of testing
• Sideloading: enabled
• Developer Mode: enabled
• S Mode: not enabled
• No prior Claude installation on this machine (fresh install attempt)

This issue matches several other reports of the same HRESULT on the same build number:

• #60319 (Claude Desktop MSIX installation fails with HRESULT 0x80073CFF on Windows 11 Pro)
• #58174 (MSIX installation fails with HRESULT 0x80073CFF after previous uninstall — Windows 11 Pro 26200)
• #53634 (Claude Desktop installation fails with HRESULT 0x80073CFF on Windows 11)
• #64029 (Claude Desktop MSIX installation fails with HRESULT 0x80073CFF on Windows 11 Pro Build 26200 — all workarounds exhausted)

All of these reports are on build 26200 specifically, which suggests a possible compatibility issue between this Windows build and the current MSIX packaging/signing used by the Claude Desktop installer, rather than a per-machine configuration problem.

Attached: ClaudeSetup.log (multiple installation attempts, most recent at end of file), screenshots of both error dialogs.

Request: since the MSIX path appears to reliably fail on this build, please make the "install without Cowork" fallback trigger automatically after an AddPackage failure, rather than requiring manual action after the error dialog.