[BUG] "illegal hardware instruction" on CPU without AVX2 (Xeon E5 v2)

[lmacchiavelli]

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?

Claude Code crashes immediately with "zsh: illegal hardware instruction" on macOS 12 with Intel Xeon E5-2697 v2 CPU.

This CPU (Ivy Bridge, 2013) does not support AVX2 instructions:

• sysctl -a | grep avx2 returns hw.optional.avx2_0: 0

Claude Code worked fine until recently. After updating, all versions from 1.0.x fail with this error.

Older versions (0.2.40) launch but cannot connect because server requires 1.0.88+.

Environment:

• macOS 12 Monterey
• CPU: Intel Xeon E5-2697 v2 (no AVX2)
• Node: v18.x (via nvm)

Request: Please provide builds without AVX2 requirement, or document minimum CPU requirements.

What Should Happen?

Claude Code should launch and run normally on CPUs without AVX2 support.

Error Messages/Logs

$ claude
zsh: illegal hardware instruction  claude

$ sysctl -n machdep.cpu.brand_string
Intel(R) Xeon(R) CPU E5-2697 v2 @ 2.70GHz

$ sysctl -a | grep avx2
hw.optional.avx2_0: 0

Steps to Reproduce

Steps to Reproduce:

1. Have a Mac with CPU without AVX2 support (e.g., Intel Xeon E5-2697 v2)
2. Install Claude Code: npm install -g @anthropic-ai/claude-code
3. Run: claude
4. Error appears: "zsh: illegal hardware instruction claude"

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

No response

Claude Code Version

Cannot run claude --version (crashes with illegal hardware instruction). Installed version: 1.0.88 (latest via npm)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

No response

[github-actions]

Found 3 possible duplicate issues:

1. [BUG] illegal hardware instruction, please compile without the AVX2 requirement #5864
2. Claude Code v2.0.27 fails with SIGILL on Intel Mac without AVX2 support #10408
3. [BUG] Unable to use Claude Code v2.1.17 on Older [2019] Intel Macs #20435

This issue will be automatically closed as a duplicate in 3 days.

• If your issue is a duplicate, please close it and 👍 the existing issue instead
• To prevent auto-closure, add a comment or 👎 this comment

🤖 Generated with Claude Code

[andrewfb]

Seeing the same, illegal instructions on late 2013 Mac Pro, 2.7 GHz 12-Core Intel Xeon E5. Manifests with both curl install and brew.

[Jachimo]

I think this is the same underlying issue as #5864, apparently the "native" builds are compiled with AVX2, while the npm version uses a node.js that's appropriate for the actual hardware (I presume).

[briankelley]

Workaround for AVX/CPU Crash. These instructions are for linux which will probably translate. I dunno. I'm not a mac guy.

The crash is caused by the bundled Bun runtime (Bun Canary v1.3.9) attempting to use AVX instructions despite being compiled as "baseline" (no_avx). This affects VMs and older CPUs that don't expose AVX.

Affected versions: 2.1.37+ (including current latest 2.1.39)
Working versions: 2.1.29 (current stable), 2.1.7 (haven't fully tested others)

---

Step 1: Get a working version

Stop using the installer - it downloads the broken latest build first, so you can't even downgrade. Grab a working version directly:

curl -fsSL -o ~/.local/share/claude/versions/2.1.29 "https://storage.googleapis.com/claude-code-dist-86c565f3-f756-42ad-8dfa-d59b1c096819/claude-code-releases/2.1.29/linux-x64/claude"

chmod +x ~/.local/share/claude/versions/2.1.29

Delete the symlink and use an alias instead (the installer keeps recreating that symlink pointing to latest):

rm ~/.local/bin/claude

Add to ~/.bashrc
alias claude='/home/YOUR_USER/.local/share/claude/versions/2.1.29'

---

Step 2: Switch to the stable release channel

Once you have a working version running, switch from latest to stable so future updates don't pull broken builds:

Run /config inside Claude and change your release channel, or edit the config directly:

Edit ~/.claude/settings.json or ~/.claude/settings.local.json

{
"releaseChannel": "stable"
}

---

Step 3: Lock it down

Environment variables (results may vary - these didn't fully prevent automatic updates for me):
export CLAUDE_CODE_DISABLE_AUTOUPDATE=1
export CLAUDE_AUTO_UPDATE=0

The most reliable method I found is locking the versions directory:
chmod 500 ~/.local/share/claude/versions/

This prevents Claude from writing new binaries. When you want to update, unlock it temporarily, download the version you want, then lock it again.

All of the above instructions were the result of me screwing around with this all day. I can appreciate a high velocity CI/CD pipeline that forces EVERY SINGLE USER TO BE BETA TESTERS (e.g. 'latest'), but when you release a breaking version where it's not clear how to revert because the installation process downloads the broken version in order to downgrade, that's an incredibly myopic approach.

[Jachimo]

Since 5864 was closed (erroneously, in my view, but whatever) by a bot, this seems to be the issue for the missing-stair AVX requirement in the Bun runtime in releases 2.1.37 - 2.1.39 (at least).

[seanconrad1]

I'm running into the exact same issue as well on a 2012 Macmini, haven't found a version that works for me just yet

[barthel]

I have the same error on my Mac Pro 6,1 with version 2.1.50.

I tried the homebrew installation and also the installation via the installer (curl -fsSL https://claude.ai/install.sh | bash). The same error occurred with both variants.

But the Node.js installation works
❯ npm install -g @anthropic-ai/claude-code
❯ claude

Welcome to Claude Code v2.1.50

---

1. ❯ brew install --cask claude-code

==> Downloading https://storage.googleapis.com/claude-code-dist-86c565f3-f756-42ad-8dfa-d59b1c096819/claude-code-releases/2.1.50/darwin-x64/claude
######################################################################################################################################################### 100.0%
==> Installing Cask claude-code
==> Linking Binary 'claude' to '/usr/local/bin/claude'
🍺  claude-code was successfully installed!

2. ❯ which claude

/usr/local/bin/claude

3. ❯ claude --version

Illegal instruction: 4

macOS 15.7.4
Mac Pro 6,1 (Xeon E5, no AVX2)
❯ sysctl -n machdep.cpu.brand_string

Intel(R) Xeon(R) CPU E5-1680 v2 @ 3.00GHz

❯ sysctl -a | grep avx2

hw.optional.avx2_0: 0

❯ sysctl -a | grep machdep.cpu | grep -i avx

machdep.cpu.features: FPU VME DE PSE TSC MSR PAE MCE CX8 APIC SEP MTRR PGE MCA CMOV PAT PSE36 CLFSH DS ACPI MMX FXSR SSE SSE2 SS HTT TM PBE SSE3 PCLMULQDQ DTES64 MON DSCPL VMX SMX EST TM2 SSSE3 CX16 TPR PDCM SSE4.1 SSE4.2 x2APIC POPCNT AES PCID XSAVE OSXSAVE TSCTMR AVX1.0 RDRAND F16C

[pescoll]

Same problem in a Mac Pro 2013
Intel(R) Xeon(R) CPU E5-1620 v2 @ 3.70GHz

Edit:
Installed via npm:
npm install -g @anthropic-ai/claude-code

Running it in VS Code terminal mode (chat not working)