There are two ways to enter AST mode from normal mode: switching and “peeking”. To switch between modes, press and release the mode switch key (defaults to Esc). To peek, hold the mode switch key down while in normal mode.

The benefit of peeking is that the mode switch key can be used like a modifier key from normal mode, avoiding the overhead of a full switch-and-switch-back when you only need to issue one or two commands.