[BUG] Cowork crashes on M4 Mac - seccomp killed error

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?

Cowork fails to start on M4 Mac. It's using the Linux seccomp binary instead of macOS sandbox-exec.

What Should Happen?

Cowork should start normally using macOS sandbox-exec

Error Messages/Logs

CLI output was not valid JSON. This may indicate an error during startup. Output: /usr/bin/bash: line 4: 5 Killed /usr/local/lib/node_modules_global/lib/node_modules/@anthropic-ai/sandbox-runtime/vendor/seccomp/arm64/apply-seccomp

Steps to Reproduce

1. Open Cowork on M4 Mac
2. Error appears immediately on startup

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

N/A - using Cowork (browser), not Claude Code CLI

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

M4 Mac, sandbox-runtime updated to latest version via npm