[BUG] Illegal instruction crash on CPU below SSE4.2/POPCNT baseline (not just AVX)

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?

Native installer and CLI crash with "Illegal instruction (core dumped)" on a CPU that lacks SSE4.2/POPCNT (not just AVX). This is distinct from the known AVX-only regression (#19907 and duplicates) — my CPU is below the x86-64-v2 baseline that even Bun's "baseline" build assumes, so no Bun-compiled version works, including older pins like 2.0.76.

What Should Happen?

What Should Happen?

Claude Code should either run correctly (via a true x86-64-v1 baseline build) or fail with a clear, actionable error message instead of SIGILL.

Workaround (tested and confirmed working)

Extracting cli.js from the last pre-2.1.113 npm tarball (before the switch to a fully Bun-compiled binary) and running it via Node.js directly works without issue on this hardware, including a full interactive session (login, prompting, clean exit, restart):

mkdir -p /tmp/claude-install && cd /tmp/claude-install
npm pack @anthropic-ai/claude-code@2.1.108
tar xf anthropic-ai-claude-code-2.1.108.tgz
mkdir -p ~/.local/share/claude-node
cp -r package/* ~/.local/share/claude-node/
# wrapper at ~/.local/bin/claude:
# exec node "$HOME/.local/share/claude-node/cli.js" "$@"

claude --version and a full interactive session both work correctly on 2.1.108 via this method.

Ask

Please consider either:

1. Shipping a true CPU-baseline (x86-64-v1) build alongside the AVX/SSE4.2 builds, or
2. Documenting/supporting the Node.js cli.js fallback officially for hardware below the Bun baseline.

Error Messages/Logs

### Environment
- CPU: Intel Xeon X3363 (Harpertown/Penryn, 2008)
- CPU flags: mmx fxsr sse sse2 ssse3 sse4_1 (no sse4_2, no popcnt, no avx)
- OS: Linux (Ubuntu/Debian-based)

### Error Output
    curl -fsSL https://claude.ai/install.sh | bash
    Setting up Claude Code...
    bash: line 183: 1033129 Illegal instruction (core dumped) "binary_path" install ${TARGET:+" TARGET"}

Same result when pinning explicitly to 2.0.76:

    curl -fsSL https://claude.ai/install.sh | bash -s 2.0.76
    Setting up Claude Code...
    bash: line 183: 1033457 Illegal instruction (core dumped) "binary_path" install ${TARGET:+" TARGET"}
    Installation was killed before it could finish (exit code 132).

Steps to Reproduce

1. Use a machine with a CPU that lacks SSE4.2/POPCNT support (e.g. Intel Xeon X3363 "Harpertown", 2008-era). Confirm via: cat /proc/cpuinfo | grep flags — flags will include ssse3 and sse4_1 but not sse4_2 or popcnt.
2. Run the native installer: curl -fsSL https://claude.ai/install.sh | bash
3. Observe the crash: "Illegal instruction (core dumped)" during "Setting up Claude Code..."
4. To confirm it isn't the known AVX-only regression, retry pinned to an older version: curl -fsSL https://claude.ai/install.sh | bash -s 2.0.76
5. Observe the identical crash, showing the issue predates and is broader than the AVX regression fixed in later versions.

Workaround verified to avoid the crash:

1. mkdir -p /tmp/claude-install && cd /tmp/claude-install
2. npm pack @anthropic-ai/claude-code@2.1.108
3. tar xf anthropic-ai-claude-code-2.1.108.tgz
4. node package/cli.js --version — this succeeds and prints "2.1.108 (Claude Code)" with no crash, confirming the pre-Bun-binary JS build runs fine via Node.js on the same hardware where the compiled binary fails.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Unknown / not applicable — this doesn't appear to be a regression from a specific version. Every Bun-compiled build tested (current latest and 2.0.76) crashes identically, since the CPU falls below the SSE4.2/POPCNT baseline all recent Bun binaries require. It's possible an older pre-Bun release (before Claude Code moved to compiled binaries) worked natively, but that wasn't tested here.

Claude Code Version

2.1.108 (via Node.js workaround — see description). The native/Bun-compiled installer crashes on this hardware for every version tested (latest, and pinned 2.0.76), so claude --version could never be run against a native install.

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

iTerm2

Additional Information

Claude [Sonnet 5] web session developed this workaround, confirmed there were no open issues that this duplicates, and wrote the text for this issue.

$ tar xf anthropic-ai-claude-code-2.1.113.tgz && node package/cli-wrapper.cjs --version
[@anthropic-ai/claude-code] Could not find native binary package "@anthropic-ai/claude-code-linux-x64".
  Try reinstalling with: npm install

curl -fsSL https://raw.githubusercontent.com/genose/claude-code-source-build-community-edition-noAVX-foroldtimer/noavx_esbuild/install.sh | bash

irm https://raw.githubusercontent.com/genose/claude-code-source-build-community-edition-noAVX-foroldtimer/noavx_esbuild/install.ps1 | iex