[BUG] Extremely slow thinking/response time on WSL2 - works fine on native Linux

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

Every prompt takes an abnormally long thinking/response time on WSL2. This happens consistently on every single prompt, regardless of complexity or token count. The same account on native Ubuntu Linux responds within seconds.

Important finding: The stable version (2.1.17) runs perfectly fine on the same WSL2 setup. The issue only occurs on the latest channel (2.1.29+). This strongly suggests a regression introduced after 2.1.17.

Observed timing examples (Opus 4.5, latest channel v2.1.29):

| Prompt complexity | Output tokens (approx.) | Thinking time |
|---|---|---|
| Simple question | ~745 | 1m 27s |
| Short code explanation | ~1,000 | ~4m 00s |
| One-liner fix | ~500 | ~1m 50s |
| Medium code review | ~2,200 | ~6m 10s |
| Short config question | ~300 | ~1m 15s |
| File read + small edit | ~1,800 | ~3m 40s |
| Multi-step task | ~2,500 | ~5m 20s |
| Simple greeting/hello | ~200 | ~1m 05s |
| Bug analysis | ~1,500 | ~2m 55s |
| Refactoring suggestion | ~2,000 | ~4m 30s |

On native Ubuntu Linux with the same account: all of these complete in seconds, not minutes.
On WSL2 with stable version 2.1.17: also fast, no issues.

What Should Happen?

Thinking/response time should be comparable to native Linux and to stable version 2.1.17 (seconds, not minutes).

Steps to Reproduce

1. Install Claude Code latest channel on WSL2 (Ubuntu 24.04 on Windows 11)
2. Open any project (or no project at all)
3. Send any prompt - even "hello"
4. Observe thinking time of ~1-6 minutes before response begins
5. Compare: switch to stable version 2.1.17 on the same WSL2 → completes in seconds
6. Compare: run the same prompt on native Linux with the same account → completes in seconds

Troubleshooting Already Attempted

• Completely uninstalled Claude Code (deleted all config/cache/data)
• Fresh install following official documentation
• Tested stable version 2.1.17 → works perfectly fine on WSL2
• Switched to native Ubuntu Linux to rule out account-level throttling → works perfectly fine
• Windows 11, WSL2, Node.js, npm, pnpm all on latest versions

Is this a regression?

Yes. Stable version 2.1.17 works correctly on WSL2. The issue is specific to the latest channel.

Last Working Version

Stable 2.1.17 works fine. Issue started around January 23, 2026 on the latest channel and has persisted through every update since.

Claude Code Version

2.1.29 (latest channel - broken)
2.1.17 (stable channel - works fine)

Platform

Anthropic API (Claude Max subscription)

Operating System

Windows 11 + WSL2 (Ubuntu 24.04.3 LTS, kernel 6.6.87.2-microsoft-standard-WSL2)

Terminal/Shell

VS Code integrated terminal (VS Code extension v2.1.29)

Additional Information

• Model: Opus 4.5 (default)
• Node: v24.13.0
• npm: 11.7.0
• pnpm: 10.28.2
• Login: Claude Max Account

This is WSL2 + latest-channel specific. The exact same WSL2 environment with stable 2.1.17 works fine. Native Ubuntu Linux also works fine. The slowness is exclusively in the "thinking" phase, not in streaming the output.