[BUG] "4;0;" notifications appearing on Claude start and quit

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 started producing strange notifications on launch and after the /exit command.

The notification says: 4;0;.

<img width="566" height="116" alt="Image" src="https://github.com/user-attachments/assets/506f9a01-1c66-438c-a421-5cd697143230" />

I first noticed the issue after the update on January 27, 2026.

System: Ubuntu 24.04.3 LTS
Claude version: 2.1.22 (Claude Code)
Terminal: Kitty 0.32.2
Homebrew version: 5.0.12

What Should Happen?

What Should Happen? Well, I think this field should not be mandatory.

Error Messages/Logs

Steps to Reproduce

Again, making this field mandatory does not make sense.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.22 (Claude Code)

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Other

Additional Information

_No response_