[BUG] Regression: Claude Code crashes with SIGILL on non-AVX CPU (macOS 12.7.6, 2.1.251) — see also #19907, #19904, #19967, #20611

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?

Claude Code crashes immediately on startup with a SIGILL ("Illegal instruction") error on a Mac without AVX support. This is the same underlying regression already reported in several other threads (#19907, #19904, #19967, #20611) — those are closed/locked as duplicates despite significant community reaction (18+ 👍 on #19907 alone), and the bug is still present in the current release, so I'm filing to keep visibility on it.

This also isn't just a CLI/terminal issue — the Claude Code UI in the Claude desktop app is entirely unusable on affected hardware with the latest version, since it relies on the same crashing binary.

What Should Happen?

Claude Code should launch and run normally on CPUs without AVX/AVX2 support, as it did in earlier versions (confirmed working again after downgrading to 2.1.108).

Error Messages/Logs

============================================================
Bun v1.4.1 (392624bed) macOS x64
macOS v12.7.6
CPU: sse42 popcnt
Args: "claude"
Features: jsc no_avx2 no_avx standalone_executable claude_code
Builtins: "bun:main" "node:async_hooks" "node:crypto" "node:fs" "node:fs/promises" "node:os" "node:path" "node:process"
Elapsed: 66ms | User: 32ms | Sys: 63ms
RSS: 24.88 MB | Peak: 24.88 MB | Commit: 49.1 MB | Faults: 0 | Machine: 34.36 GB

CPU lacks AVX support. Please consider upgrading to a newer CPU.
panic(main thread): Illegal instruction at address 0x11005E4D8
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

Steps to Reproduce

1. Have a Mac (or other machine) without AVX CPU support (in my case macOS 12.7.6, Intel).
2. Install/update to Claude Code 2.1.251 via npm.
3. Run claude --version or claude in iTerm2.
4. Observe immediate crash with "CPU lacks AVX support" / SIGILL, as shown in the error log above.

Workaround: sudo npm install -g @anthropic-ai/claude-code@2.1.108 restores a working install.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.108

Claude Code Version

2.1.251 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

This is a widely-reported regression from the Bun runtime switch, related reports: #19907 (18+ thumbs up, multi-platform: Linux/macOS/Windows/ARM64), #19904, #19967, #20611. All are closed as duplicates and locked, so filing this to consolidate and keep visibility since the underlying bug remains unresolved in the current release.

Requests:

• Ship a CPU-baseline Bun build (no AVX/AVX2 requirement), similar to Bun's own baseline builds.
• - Fail gracefully with a clear message instead of a hard SIGILL crash.
• - - Document minimum CPU requirements for native/npm installs.

Workaround confirmed: downgrading to 2.1.108 via npm resolves the crash.