[BUG] Claude Code uses legacy XTMODKEYS even when terminal advertises the kitty keyboard protocol

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?

Environment

• Claude Code: 2.1.150
• Terminal: kitty 0.41.1
• OS: Debian 13 (trixie), x86_64
• Shell: bash

Summary

When Claude Code runs inside kitty, it negotiates input handling via xterm's legacy modifyOtherKeys (XTMODKEYS — CSI > 4 ; 2 m) instead of using kitty's
enhanced keyboard protocol. Kitty advertises support for its own protocol and emits a diagnostic recommending the app switch.

Observed

Kitty prints, repeatedly:

The application is trying to use xterm's modifyOtherKeys. This is superseded
by the kitty keyboard protocol https://sw.kovidgoyal.net/kitty/keyboard-protocol.
The application should be updated to use that.
[PARSE ERROR] CSI code m has 2 > 1 parameters

The pattern correlates with focus/input re-initialisation, suggesting Claude Code re-asserts input modes after focus-in or idle wake.

What Should Happen?

Expected

When the terminal responds positively to the kitty keyboard protocol query (CSI ? u), Claude Code should use it instead of falling back to / additionally
sending XTMODKEYS, eliminating both the kitty diagnostic and the CSI parse warning.

Error Messages/Logs

[PARSE ERROR] CSI code m has 2 > 1 parameters

Steps to Reproduce

1. Launch kitty (0.41.x).
2. Run claude (2.1.150) inside it.
3. Interact normally, then either:

• move focus away and back (focus-follows-mouse setups will trigger it just by mousing over another window), or
• leave the window idle for a few seconds and resume typing.

1. Observe ~/.xsession-errors.

Impact

Cosmetic — input still works correctly. Reporting because (a) it pollutes .xsession-errors and any session log file, and (b) it indicates Claude Code isn't
taking advantage of the richer key-event reporting that kitty's protocol provides (Ctrl+letter disambiguation, key-release events, etc.).

References

• Kitty keyboard protocol: https://sw.kovidgoyal.net/kitty/keyboard-protocol/
• XTMODKEYS spec: https://invisible-island.net/xterm/manpage/xterm.html (search modifyOtherKeys)

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude Code: 2.1.150

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Other

Additional Information

_No response_