Subchamber 4 is a room in the Impact Crater in Metroid Prime. It is the fourth and final battle within the subchambers of the crater, where Metroid Prime in its exoskeleton form is fought. In this subchamber, Metroid Prime will use all four beam color attacks, randomly switching between them at will, making it more difficult to cause damage quickly. When damaged enough, it will fall through into Subchamber 5 and down into the Metroid Prime Lair.
In the NTSC version of the game, three tunnel grooves exist in the ground that allow Samus to avoid Metroid Prime when it runs across the room, but in the PAL and Trilogy versions, all but the middle groove have been removed.