claude-code [BUG] Windows Update KB5074109 Breaks Claude Code

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?

I have been using CC native install on Windows 11 (ARM) for many months.

Yesterday, Windows Update ran KB5074109. After this update was installed, claude code would not start and would say "Segmentation fault" whenever invoked.

Thinking that maybe my CC installation was corrupted, I completely uninstalled CC and then tried reinstalling using the PowerShell script for Windows native install. The script would complete successfully but the binary would not get written to the .local\bin directory. (Similar to #18183)

I manually uninstalled Windows update KB5074109, after which, CC was able to install and run fine.

I believe this may be related to x64 emulation on ARM64 Windows, as I do not have this issue on my native x64 machine.

KB5074109 is labeled by Microsoft as a required security update, so my corporate AD-joined computer doesn't have the ability to uninstall this update, and I imagine many other users will have this update installed automatically in the coming days.

What Should Happen?

Claude Code should install and/or run normally as it did prior to the installation of KB5074109.

Error Messages/Logs

Checking installation status...
Exit code: -1073741819 (Access violation)

AzureAD+RedactedUser@DEV-PC CLANGARM64 /c/LocalRepositories/RedactedPath
$ claude
Segmentation fault

Steps to Reproduce

Run windows update KB5074109 and then try to install or run CC on Windows 11 ARM.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

No response

Claude Code Version

2.1.7

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

No response

Jan 14 '26 23:01 rfmsanz-ethan

ran into this all day working on electrobun, i thought I was losing my mind. Claude code doesn't open, but also the electrobun cli (which is a bun sfe) also exits with code 5.

I just reported this over at https://github.com/oven-sh/bun/issues/26150 before I found this issue

I'm in a windows ARM vm on a macbook m4 host, so windows x64 isn't an option.

I ran this in a powershell and restarted, and then reinstalled bun and then claude and bun/electrobun cli both work again

wusa /uninstall /kb:5074109

gonna go think about how microsoft just sent me down this rabbit hole on the day I was finishing up windows compatibility for Electrobun v1

Jan 15 '26 23:01 YoavCodes

Same. Glad to see I'm not alone out there. My colleagues and I also use Windows 11 in Parallels on M4 Pro Mac Minis.

Jan 16 '26 00:01 rfmsanz-ethan

Glad I'm not alone, would love a fix though

The VSCode claude extension still works, but cant reference folders in it so feels gimped

Jan 16 '26 13:01 sitefinitysteve

Confirming this issue on Windows 11 ARM64 in Parallels Desktop (Mac host)

Environment:

Host: MacBook Air M4
VM: Windows 11 ARM64 via Parallels Desktop
Claude Code: Native installer (latest)
Error: Segmentation fault immediately when running claude

Observations:

claude --version and claude --help work fine
Any actual execution (e.g., claude doctor, claude -p "test") crashes with segfault
Windows Update KB5074109 is installed (cannot uninstall on most systems)

Working workaround:

npm install -g @anthropic-ai/claude-code

The npm installation works without issues, confirming this is specific to the native binary + x64 emulation on ARM64.

Request: A native win32-arm64 binary would resolve this permanently. With the growing adoption of ARM64 Windows devices (Surface Pro, Snapdragon X Elite laptops, Parallels VMs on Apple Silicon), native ARM64 support is increasingly important.

Feb 08 '26 21:02 Shmehade321

Starting last night CC on Parallels, without the KB installed (have an uninstall script I use to keep it off)... it just refuses to load now, well I see the interface, then it crashes a few seconds later.

So fun

Feb 12 '26 12:02 sitefinitysteve

v2.1.41 today

Added Windows ARM64 (win32-arm64) native binary support

Feb 13 '26 14:02 sitefinitysteve

@sitefinitysteve Thanks for the update, I appreciate it. Have you tested to see if it's working as expected?

Feb 13 '26 14:02 Shmehade321

Moved back to native from NPM, she's not crashing here, says I have all my windows updates, Latest Parallels on M3 Max Windows 11 ARM. Cautiously optomitic.

Feb 13 '26 14:02 sitefinitysteve

Does that mean win32-arm64 releases are coming?

Pete Microsoft

Feb 13 '26 20:02 Psychlist1972

It’s here

Feb 13 '26 21:02 sitefinitysteve

Thanks. I really asked the wrong question.

Are fully functional windows Arm64 builds, equivalent to macOS functionality, coming as a result of this?

Thanks.

Feb 13 '26 21:02 Psychlist1972

Claude Code (the CLI) is now available for Windows ARM64 via install.ps1, install.cmd, and winget - see https://code.claude.com/docs/en/quickstart#step-1-install-claude-code (starting with version 2.1.41 for installer scripts, 2.1.42 for winget)

Bringing local sessions to Claude Code on desktop for Windows ARM64 - we're working on this!

Feb 17 '26 21:02 ant-kurt

Fantastic! Thank you :)

Pete Microsoft

Feb 18 '26 21:02 Psychlist1972

On this, did you create your own Bun Arm64 release, or is Bun not a dependency for the CLI?

Pete Microsoft

Feb 18 '26 21:02 Psychlist1972

My recollection is that they use node.js not bun.

Feb 18 '26 21:02 rfmsanz-ethan

Actually, I take that back. Using the current CC ARM64 2.1.47 (native install) shows: Bun v1.3.10 (1423d3c8) Windows arm64

Feb 18 '26 22:02 rfmsanz-ethan

That's unexpected. On the Bun repo, it shows as still not building for Windows. Maybe a late fix?

Pete Microsoft

Feb 18 '26 22:02 Psychlist1972

From Bun's blog:

Windows ARM64

We've added JIT & interpreter support for Windows ARM64 to JavaScriptCore. This was the main blocker for unblocking Windows ARM64 support in Bun. We don't yet support Windows ARM64 in Bun, but it's coming soon.

Feb 18 '26 22:02 rfmsanz-ethan