[BUG] Fresh install from claude.com/download resulted in Squirrel install, not MSIX — no errors shown, blocked Cowork

[exaclast]

Preflight Checklist

• I have searched existing issues and this hasn't been reported yet
• This is a single bug report (please file separate reports for different bugs)
• I am using the latest version of Claude Code

What's Wrong?

Installed Claude Desktop fresh from claude.com/download within the last month (no prior installation on this machine, no upgrade scenario). Setup completed with no errors or warnings shown. Result was a Squirrel-based install rather than MSIX:

• %LocalAppData%\AnthropicClaude contained a SquirrelTemp folder, update.exe, and app-<version>/squirrel.exe — Squirrel's standard layout
• Get-AppxPackage | Where-Object {$_.Name -like "*Claude*" -or $_.Name -like "*Anthropic*"} returned nothing — no MSIX registration at all

Notably, no UAC/administrator elevation prompt appeared during install — per Anthropic's own docs, admin privileges are required for full Cowork support, so a non-elevated install path may be the actual mechanism here rather than a silent MSIX→Squirrel fallback.

Impact: Cowork was inaccessible, showing "Cowork requires Claude Desktop be installed with our modern installer." A full uninstall + reinstall from the same download page reproduced the same Squirrel result.

Ruled out as the cause:

• Windows Virtual Machine Platform was already enabled (Get-WindowsOptionalFeature -Online -FeatureName VirtualMachinePlatform confirmed Enabled before any changes)
• Not a legacy-install carryover — this was a first-time install on this machine

Unknown: whether the lack of elevation caused the installer to skip MSIX entirely, or whether MSIX was attempted and fell back silently for another reason. Setup/bootstrapper logs were not preserved (the install folder was cleared during troubleshooting before this was known to matter), so the exact mechanism can't be confirmed from this report alone — but the missing UAC prompt is a plausible lead.

Fix that worked: manually locating and installing the MSIX package directly (not linked from the main download page) resolved the issue and enabled Cowork.

Possibly related: #62116, #25162, #28998 — similar Squirrel/MSIX mismatches, though those involve upgrade scenarios or explicit install failures rather than a silent fresh-install outcome.

What Should Happen?

A fresh install from the main download page (claude.com/download) should reliably result in an MSIX-based install with Cowork available — or, if it falls back to Squirrel for any reason, the installer should surface that to the user rather than completing silently as if successful.

Error Messages/Logs

None shown during setup. In-app error when opening Cowork: "Cowork requires Claude Desktop be installed with our modern installer."

Steps to Reproduce

1. Go to claude.com/download and download the Windows installer
2. Run the installer — no UAC/admin elevation prompt appeared
3. Complete setup — no errors shown, app launches normally
4. Open Claude Desktop → Cowork tab
5. Observe: "Cowork requires Claude Desktop be installed with our modern installer"
6. Check %LocalAppData%\AnthropicClaude — SquirrelTemp folder present
7. Run Get-AppxPackage | Where-Object {$_.Name -like "*Claude*"} — returns nothing

Claude Model

None

Is this a regression?

I don't know

Last Working Version

No response

Claude Code Version

1.22209.3

Platform

Other

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

Workaround: manually downloading and installing the MSIX package directly (not the one linked from the main download page) fixed the issue.

[labolabo]

Confirmed the root cause and a working workaround on Windows 10 Pro (build 19045).

The in-app message "Cowork requires Claude Desktop be installed with our modern installer" corresponds to unsupportedCode: "msix_required" (visible in the app bundle). The Squirrel (.exe) build can never enable Cowork — no matter how many times you reinstall from the official download page, which currently serves that Squirrel exe.

Workaround that worked for me:

1. Fetch the MSIX package directly: https://claude.ai/api/desktop/win32/x64/msix/latest/redirect
2. Install from an elevated PowerShell: Add-AppxPackage -Path .\Claude-<hash>.msix — elevation is required because the package contains packaged services (without it you get 0x80073D28)
3. Close the Squirrel app and launch the packaged app (AUMID Claude_pzs8sxrjxfjjc!Claude)
4. Optionally uninstall the Squirrel build (%LocalAppData%\AnthropicClaude\Update.exe --uninstall) and delete its Claude entry under HKCU\Software\Microsoft\Windows\CurrentVersion\Run, otherwise the wrong build keeps auto-launching at boot

After switching, %AppData%\Claude\logs\cowork_vm_node.log goes from yukonSilver not supported (status=unsupported) to a successful VM bootstrap, and Cowork works normally.

Two papercuts that would prevent others from hitting this:

• The download page serves an .exe that cannot run Cowork, with no in-app upgrade path to MSIX
• Localization: the Japanese UI renders "modern installer" as 「最新のインストーラー」 ("latest installer"), which sends users into endless reinstall loops with the same exe