[BUG] Bun crashes with "CPU lacks AVX support. Please consider upgrading to a newer CPU."

Found 3 possible duplicate issues:

1. https://github.com/anthropics/claude-code/issues/7107
2. https://github.com/anthropics/claude-code/issues/5864
3. https://github.com/anthropics/claude-code/issues/13894

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🤖 Generated with Claude Code

❯ claude
============================================================
Bun v1.3.6 (d530ed99) Linux x64 (baseline)
Linux Kernel v6.18.5 | glibc v2.42
Args: "claude"
Features: Bun.stderr(2) Bun.stdin(2) Bun.stdout(2) fetch(20) jsc no_avx2 no_avx spawn(20) standalone_executable
Builtins: "bun:main" "node:assert" "node:async_hooks" "node:buffer" "node:child_process" "node:constants" "node:crypto" "node:domain" "node:events" "node:fs" "node:fs/promises" "node:http" "node:https" "node:module" "node:net" "node:os" "node:path" "node:path/posix" "node:path/win32" "node:perf_hooks" "node:process" "node:querystring" "node:stream" "node:timers/promises" "node:tls" "node:tty" "node:url" "node:util" "node:zlib" "node:worker_threads" "undici" "ws" "node-fetch" "node:inspector" "node:http2" "node:diagnostics_channel"
Elapsed: 935ms | User: 812ms | Sys: 145ms
RSS: 1.20GB | Peak: 0.43GB | Commit: 1.20GB | Faults: 0 | Machine: 8.31GB

CPU lacks AVX support. Please consider upgrading to a newer CPU.
panic(main thread): Illegal instruction at address 0x4001FB4
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

I'm seeing the same problem, where claude was working fine earlier today.

Please stop using claude code for generating claude code.

Technical Details:

1. Runtime Change: Claude Code 2.1.15 switched from Node.js to Bun as its JavaScript runtime
2. Bun's AVX Requirement: Bun's JavaScript engine (JavaScriptCore) uses AVX instructions for performance optimizations and crashes when these are unavailable
3. Virtualization Impact: Common hypervisors (QEMU/KVM, VirtualBox, VMware) often use generic CPU models by default that don't expose AVX flags to guest VMs
4. Breaking Change: Previous Node.js-based versions worked without AVX support

Why This Happens in VMs:

• Default QEMU CPU types like qemu64 or kvm64 only expose baseline x86-64 instructions
• AVX support requires either:
• Passing through the host CPU type (-cpu host)
• Using a CPU model that includes AVX (e.g., SandyBridge, Haswell, or newer)

Resolution / Workaround

For Proxmox/QEMU users:

1. Shut down the VM
2. Edit the VM configuration to use host CPU passthrough:

• In Proxmox UI: VM → Hardware → Processor → Type → Select "host"
• Or via CLI: qm set <vmid> -cpu host

1. Start the VM

For other hypervisors:

• VirtualBox: Ensure "Enable Nested VT-x/AMD-V" is enabled and use a modern CPU profile
• VMware: Use "Virtualize Intel VT-x/EPT or AMD-V/RVI" option

Verified Working: After changing the CPU type to host, Claude Code 2.1.15 launches successfully.

Check AVX availability:

grep -o 'avx[^ ]*' /proc/cpuinfo | head -1
# Should output: avx avx2 (or similar)

Same issue here - VPS users completely locked out
I'm experiencing the exact same crash on my VPS (Debian, Linux Kernel 6.1.0). Claude Code worked fine until yesterday, then after an automatic update it stopped working entirely.

CPU lacks AVX support. Please consider upgrading to a newer CPU.
panic(main thread): Illegal instruction at address 0x4001FB4

The problem is: I cannot upgrade the CPU. This is a hosted VPS where I have no control over the hypervisor or CPU type. Many VPS providers use older Xeon generations or don't expose AVX instructions to guests.

This effectively locks out a significant portion of users who:

• Use VPS/cloud servers for development
• Run older but still perfectly capable hardware
• Have no control over their virtualization layer

Suggested fix:
Please provide a baseline build without AVX dependency, similar to what Bun offers (bun-linux-x64-baseline). AVX should be an optimization, not a hard requirement.
This is a regression that broke a previously working setup overnight. Would appreciate a quick fix or at least a way to pin to an older working version.

Thanks @ul0gic I'll try these steps and report back.

Same issue here on v2.1.15. Rolled back to 2.1.14 and working again.
Hope this bug gets fixed in Bun.

I resolved this issue by downgrading to v2.1.14. Installation instructions for specific versions can be found here: https://code.claude.com/docs/en/getting-started

Technical Details: 1. Runtime Change: Claude Code 2.1.15 switched from Node.js to Bun as its JavaScript runtime 2. Bun's AVX Requirement: Bun's JavaScript engine (JavaScriptCore) uses AVX instructions for performance optimizations and crashes when these are unavailable 3. Virtualization Impact: Common hypervisors (QEMU/KVM, VirtualBox, VMware) often use generic CPU models by default that don't expose AVX flags to guest VMs 4. Breaking Change: Previous Node.js-based versions worked without AVX support Why This Happens in VMs: Default QEMU CPU types like qemu64 or kvm64 only expose baseline x86-64 instructions AVX support requires either: Passing through the host CPU type (-cpu host) Using a CPU model that includes AVX (e.g., SandyBridge, Haswell, or newer) ### Resolution / Workaround For Proxmox/QEMU users: 1. Shut down the VM 2. Edit the VM configuration to use host CPU passthrough: In Proxmox UI: VM → Hardware → Processor → Type → Select "host" Or via CLI: qm set <vmid> -cpu host 3. Start the VM For other hypervisors: VirtualBox: Ensure "Enable Nested VT-x/AMD-V" is enabled and use a modern CPU profile VMware: Use "Virtualize Intel VT-x/EPT or AMD-V/RVI" option Verified Working: After changing the CPU type to host, Claude Code 2.1.15 launches successfully. Check AVX availability: grep -o 'avx[^ ]*' /proc/cpuinfo | head -1 # Should output: avx avx2 (or similar)

This worked for me. Proxmox user here. Thanks @ul0gic

Workaround for "CPU lacks AVX support" crash on Proxmox VMs

For users running Claude Code on Proxmox VMs with CPU type kvm64 (or similar virtual CPUs without AVX support), changing the CPU type to host or another AVX-capable type is not always an option — especially when VM portability across different Proxmox hosts is required.

1. Downgrade Claude Code via npm (version 2.1.11)

The npm installation does not use Bun and therefore has no AVX requirement:

npm install -g @anthropic-ai/claude-code@2.1.11

Verify the installation:

claude --version

To prevent auto-updates, add to ~/.claude/settings.json:

{
  "env": {
    "DISABLE_AUTOUPDATER": "1"
  }
}

2. Downgrade VS Code Extension

The VS Code extension also needs to be downgraded:

1. Open VS Code
2. Go to Extensions sidebar
3. Find "Claude Code"
4. First: Uncheck "Auto Update" in the extension
5. Click the dropdown arrow next to "Uninstall"
6. Select "Install Another Version..."
7. Choose version 2.1.11

This combination works on Proxmox VMs without AVX support.

See also #20019

The dame problem here, Linux runing under Oracle vm

Consolidating onto #19907

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