[BUG] AVX warning on startup: CPU lacks AVX support, Bun baseline build needed

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?

When running the claude command to start Claude Code, I receive a warning message:

"warn: CPU lacks AVX support, strange crashes may occur. Reinstall Bun or use *-baseline build:
https://github.com/oven-sh/bun/releases/download/bun-v1.3.5/bun-darwin-x64-baseline.zip"

This appears to be caused by Claude Code's bundled Bun runtime being incompatible with CPUs that don't support AVX (Advanced Vector Extensions) instructions.

What Should Happen?

Claude Code should either:

1. Bundle the baseline build of Bun that works without AVX support, or
2. Detect CPU capabilities at install time and select the appropriate Bun build, or
3. Not show the warning if the tool is functioning correctly despite lack of AVX support

The tool should work without warnings on all supported macOS systems.

Error Messages/Logs

warn: CPU lacks AVX support, strange crashes may occur. Reinstall Bun or use *-baseline build:
https://github.com/oven-sh/bun/releases/download/bun-v1.3.5/bun-darwin-x64-baseline.zip

Steps to Reproduce

1. Install Claude Code on a Mac with a CPU that lacks AVX support
2. Run claude command
3. Warning appears on every startup

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.5

Claude Code Version

2.1.7

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Additional Information:

• Running npm update -g @anthropic-ai/claude-code shows the package is already up to date
• The warning mentions Bun v1.3.5, suggesting Claude Code bundles this specific version
• This affects users with older Intel Macs that don't support AVX instructions
• The tool appears to function despite the warning, but the message is concerning to users

Let me know your Claude Code version and I can update that field for you