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CSI u Key Encoding
The fixterms/CSI u encoding reports keypresses as CSI codepoint ; modifiers u sequences. This was the precursor to the Kitty keyboard protocol and provides unambiguous key identification for terminal applications.
How this is tested: Query keyboard mode flags and check if the terminal supports CSI u encoding for key events.
Analysis2026-03-26
Supported by 7 of 8 terminals (88%). Not supported by: Cursor. Part of the Modern TUI baseline.
Supported by 12 of 13 backends (92%)
Terminal Applications
| Terminal | Version | Support | Notes |
|---|---|---|---|
| iTerm2 | 3.6.9 | ✓ yes | |
| Ghostty | 1.3.1 | ✓ yes | |
| VS Code | 1.112.0 | ✓ yes | |
| Warp | 0.2026.03.18.08.24.03 | ✓ yes | |
| Cursor | 2.6.21 | ✓ yes | |
| tmux | 3.6a | ✓ yes | |
| Kitty | 0.46.2 | ✓ yes | |
| Terminal.app | 2.15 | ✓ yes | |
| GNU Screen | 5.0.1 | ✓ yes |