[BUG] Claude Code v2.1.49 crashes on Windows ARM64 with "panic: incorrect alignment" (Bun v1.3.10 bug)

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 consistently crashes on Windows 11 ARM64 with the error:
panic(thread 13708): incorrect alignment

This occurs when launching Claude Code CLI in any project directory. The crash is caused by Bun v1.3.10 running on Windows ARM64 architecture.

Error details:

• Bun v1.3.10 (1423d3c8) Windows arm64
• Windows v.win11_dt
• CPU: neon fp aes crc32 atomics
• Args: "C:\Users\jno\.local\bin\claude.exe"

The crash report link: https://bun.report/1.3.10/W_11423d3cmgkgE+gogCwmzrfwwijkBgsjufCYKERNEL32.DLLg0jCCSntdll.dlloqi1BA0eNrLzEvOLypKTS5RSMzJTM/LTc0rAQBMcwep

What Should Happen?

Claude Code should launch without crashing and allow normal interaction with the project.

Error Messages/Logs

Bun v1.3.10 (1423d3c8) Windows arm64                                                                                   
Windows v.win11_dt
CPU: neon fp aes crc32 atomics
Args: "C:\Users\jno\.local\bin\claude.exe"
Features: Bun.stderr(2) Bun.stdin(2) Bun.stdout(2) WebSocket fetch(33) jsc spawn(10) standalone_executable process_dlopen(3) yaml_parse(2) 
Builtins: "bun:main" "node:assert" "node:async_hooks" "node:buffer" "node:child_process" "node:constants" "node:crypto" "node:dns" "node:events" "node:fs" "node:fs/promises" "node:http" "node:https" "node:module" "node:net" "node:os" "node:path" "node:path/posix" "node:path/win32" "node:perf_hooks" "node:process" "node:stream" "node:timers/promises" "node:tls" "node:tty" "node:url" "node:util" "node:zlib" "node:worker_threads" "undici" "ws" "node:http2" 
Elapsed: 11982ms | User: 2781ms | Sys: 1906ms
RSS: 0.63GB | Peak: 0.64GB | Commit: 0.85GB | Faults: 221252 | Machine: 33.74GB

panic(thread 13708): incorrect alignment
oh no: Bun has crashed. This indicates a bug in Bun, not your code.

To send a redacted crash report to Bun's team,
please file a GitHub issue using the link below:
https://bun.report/1.3.10/W_11423d3cmgkgE+gogCwmzrfwwijkBgsjufCYKERNEL32.DLLg0jCCSntdll.dlloqi1BA0eNrLzEvOLypKTS5RSMzJTM/LTc0rAQBMcwep

Steps to Reproduce

1. Install Claude Code v2.1.49 on Windows 11 ARM64
2. Open PowerShell or CMD
3. Navigate to any project directory: cd C:\Users\....
4. Run: claude
5. Crash occurs immediately with "panic(thread): incorrect alignment"

This happens consistently on every launch.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Unknown (recently started occurring after installing Claude Code v2.1.49)

Claude Code Version

2.1.49 (Stable release)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

System Information:

• OS: Windows 11 ARM64
• CPU: ARM64 with neon, fp, aes, crc32, atomics support
• Claude Code: v2.1.49
• Bun: v1.3.10 (bundled with Claude Code)

Workaround tested:

• Tried reinstalling Claude Code → still crashes
• Tried running "bun upgrade" → command not found (Bun not in PATH)
• Created .claude/config.json with {"runtime": "node"} → didn't prevent crash (Claude CLI itself uses Bun internally)

Root cause:
This is a known Bun v1.3.10 bug on Windows ARM64 architecture. The issue is in the bundled Bun runtime within Claude Code, not in user project code.

Suggested fix:
Update bundled Bun version in Claude Code to v1.3.11 or later (when available) that includes the ARM64 alignment fix.