[BUG] darwin-x64 binary requires AVX2 since 2.1.113 — please ship bun-darwin-x64-baseline (like Linux/Windows already do)

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?

Starting with version 2.1.113, Claude Code switched from a Node.js JS bundle to a Bun-compiled native binary distributed per platform via optionalDependencies (@anthropic-ai/claude-code-{darwin,linux,win32}-{x64,arm64}).

The darwin-x64 binary was packaged with the non-baseline Bun variant, which requires AVX2 (Haswell, 2013+). The linux-x64 and win32-x64 binaries use Bun baseline, which only requires SSE4.2 (Nehalem, 2008+).

As a result, Claude Code >= 2.1.113 no longer runs on pre-Haswell Intel Macs (Mac Pro 2013, MacBook Pro / iMac pre-2013, etc.) — even though the latest version runs fine on the exact same hardware when booted into Windows or running Linux.

The asymmetry is a packaging decision, not a hardware/Bun limitation: the baseline variant for macOS x64 exists upstream (bun-darwin-x64-baseline) and is even referenced inside the current darwin-x64 binary's asset table.

What Should Happen?

@anthropic-ai/claude-code-darwin-x64 should be built with the bun-darwin-x64-baseline variant — matching the policy already applied to linux-x64 and win32-x64.

That single packaging change restores compatibility with any x86_64 Mac from Nehalem (2008) onwards, with only a marginal performance cost vs. the AVX2 build. No code changes required.

Error Messages/Logs

On launch, the binary prints an "unsupported processor" message and exits (exact text not captured — the affected user downgraded to 2.1.112 to recover before logs were saved). The behavior matches Bun's standard non-baseline CPU check, which prints messages like "CPU lacks AVX support. Please consider upgrading to a newer CPU." or "Unsupported CPU (no detected SIMD instructions)" (these strings are visible inside the darwin-x64 binary via `strings`).

Steps to Reproduce

Affected hardware

Any Intel Mac with an x86_64 CPU that lacks AVX2 — e.g. Mac Pro Late 2013, Xeon E5-1650 v2 (Ivy Bridge-EP), macOS 14.8.4. Verify with:

sysctl machdep.cpu.leaf7_features | tr ' ' '\n' | grep -i avx2
# (no output on affected CPUs)

Reproduce the crash

1. On an affected Mac, install latest Claude Code:

``bash
npm install -g @anthropic-ai/claude-code@latest # currently 2.1.175
claude --version
``

1. The binary fails to start with an unsupported-processor message.
2. Downgrade restores functionality:

``bash
npm install -g @anthropic-ai/claude-code@2.1.112
`
2.1.112 is the last Node-bundle release; everything >= 2.1.113` is the Bun binary.

Confirm the packaging asymmetry

npm pack @anthropic-ai/claude-code-darwin-x64@2.1.175
npm pack @anthropic-ai/claude-code-linux-x64@2.1.175
npm pack @anthropic-ai/claude-code-win32-x64@2.1.175

tar -xzf anthropic-ai-claude-code-darwin-x64-2.1.175.tgz
tar -xzf anthropic-ai-claude-code-linux-x64-2.1.175.tgz
tar -xzf anthropic-ai-claude-code-win32-x64-2.1.175.tgz

strings package/claude    | grep -E 'Bun v1\.3\.14.*x64'
# darwin: Bun v1.3.14 (2a41ca97) macOS x64        ← non-baseline
# linux:  Bun v1.3.14 (2a41ca97) Linux x64 (baseline)
# win32:  Bun v1.3.14 (2a41ca97) Windows x64 (baseline)

Only darwin-x64 is missing the (baseline) marker.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.112 (last Node-bundle release; 2.1.113 was the first Bun binary)

Claude Code Version

2.1.175 (Claude Code) — broken on macOS x64 without AVX2. Currently pinned to 2.1.112 to keep working.

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Summary of per-platform Bun variants shipped in 2.1.175

| Platform package | Bun signature in binary | Variant |
|---|---|---|
| @anthropic-ai/claude-code-darwin-x64 | Bun v1.3.14 (2a41ca97) macOS x64 | normal (requires AVX2) |
| @anthropic-ai/claude-code-linux-x64 | Bun v1.3.14 (2a41ca97) Linux x64 (baseline) | baseline |
| @anthropic-ai/claude-code-win32-x64 | Bun v1.3.14 (2a41ca97) Windows x64 (baseline) | baseline |

Suggested fix

In the build/release pipeline for @anthropic-ai/claude-code-darwin-x64, switch the embedded Bun runtime from bun-darwin-x64 to bun-darwin-x64-baseline (the URL is already referenced inside the current binary). Same policy that's already applied to the Linux and Windows builds.

Why this matters

• Apple sold non-AVX2 Intel Macs well into 2013 (Mac Pro, late iMacs, MacBook Pros), many still in active use and running supported macOS.
• The asymmetry is surprising: the latest Claude Code runs on the affected Mac under Linux and Windows, but not macOS — even though it's the same CPU.
• The only workaround today is to pin to 2.1.112, the last Node bundle. That means no further updates on this hardware indefinitely.

Happy to attach any additional diagnostics or test a pre-release baseline build.