Portal 3 expands on the mechanics of Portal 2 In Motion, which were also included as DLC for Portal 2. The player can utilize abilities such as One to One, which allows for manipulation of held objects, and portal surfing, the movement and rotation of a portal after it is placed, alongside new features. These are best utilized through motion control, but keyboard-and-mouse controls also allow for them.
The majority of Portal 3's story is unknown, but the single-player campaign will involve testing tracks constructed by old and new Personality Cores after they run amok and take control of the facility.
A multiplayer campaign has been announced as well.
- Portal 3 would originally have focused on a different new ability of the Aperture Science Handheld Portal Device, to shoot special portal orbs through existing portals. The concept was scrapped early on, as not only did early testing indicate that it made puzzles overly confusing, but it didn't fit with the existing mechanics of portals.