extended-keys

Controls how modified keys (keys pressed together with Control, Meta, or Shift) are reported. This is the equivalent of the modifyOtherKeysxterm(1) resource.

When set to on, the program inside the pane can request one of two modes: mode 1 which changes the sequence for only keys which lack an existing well-known representation; or mode 2 which changes the sequence for all keys. When set to always, modes 1 and 2 can still be requested by applications, but mode 1 will be forced instead of the standard mode. When set to off, this feature is disabled and only standard keys are reported.

tmux will always request extended keys itself if the terminal supports them. See also the extkeys feature for the terminal-features option, the extended-keys-format option and the pane_key_mode variable.