SpawnTab

Create a new tab in the current window. The argument defines to which domain the tab belongs:

local wezterm = require 'wezterm'
local act = wezterm.action

return {
  keys = {
    -- Create a new tab in the same domain as the current pane.
    -- This is usually what you want.
    {
      key = 't',
      mods = 'SHIFT|ALT',
      action = act.SpawnTab 'CurrentPaneDomain',
    },
    -- Create a new tab in the default domain
    { key = 't', mods = 'SHIFT|ALT', action = act.SpawnTab 'DefaultDomain' },
    -- Create a tab in a named domain
    {
      key = 't',
      mods = 'SHIFT|ALT',
      action = act.SpawnTab {
        DomainName = 'unix',
      },
    },
  },
}

See SpawnCommandInNewTab for a more flexible action that allows more control over the spawned command.