[BUG] Illegal instruction: 4 (SIGILL/BMI2) on 2013 Mac Pro (Xeon E5 v2 / Ivy Bridge) — regression after 2.1.30

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?

What's Wrong?

Claude Code crashes immediately on startup with Illegal instruction: 4 on a 2013 Mac Pro. The bundled binary uses CPU instructions (BMI2 / AVX2, Haswell-era) that this machine's Intel Xeon E5 v2 (Ivy Bridge) does not support. Ivy Bridge supports AVX1 but not BMI2/AVX2, so the process is killed with SIGILL before the CLI starts.

This previously worked via npm. Rolling back fixes it (see below), so this is a packaging/build regression, not a config issue.

Last Working Version

2.1.30 runs perfectly. Reinstalling with npm install -g @anthropic-ai/claude-code@2.1.30 resolved the crash completely. The current latest build crashes. So the regression landed somewhere after 2.1.30.

Is this a regression?

Yes. 2.1.30 works; a current build does not.

Additional Information

• Machine: Mac Pro (Late 2013, "trash can")
• CPU: Intel Xeon E5 v2 (Ivy Bridge) — supports AVX1, no AVX2/BMI2
• OS: macOS 12.7.6
• Node.js: v24.12.0

What Should Happen?

A fallback binary (or x86-64-v2 baseline build) for older Intel Macs without AVX2/BMI2, or at minimum documenting the minimum CPU requirement so users know to pin an older version. Related: #19931, #50904.

Error Messages/Logs

Illegal instruction: 4
Exception Type:        EXC_BAD_INSTRUCTION (SIGILL)
Termination Reason:    Code 4 Illegal instruction

The crashing opcode reported in related issues (`c4 e2 f9 f7 d1`) is a VEX-encoded BMI2 instruction, which Ivy Bridge lacks.

Steps to Reproduce

1. On a 2013 Mac Pro (Xeon E5 v2 / Ivy Bridge), install the latest: npm install -g @anthropic-ai/claude-code
2. Run: claude
3. Immediate crash: Illegal instruction: 4
4. Workaround: npm install -g @anthropic-ai/claude-code@2.1.30 — works.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.30

Claude Code Version

Illegal instruction: 4

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_