SpawnTab

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

local act = wezterm.action

config.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.