What is the official name of the cooperative campaign in Portal 2?

The official name of Portal 2's cooperative campaign is the Cooperative Testing Initiative. It is the two-player portion of the game in which partners solve portal-based experiments together for GLaDOS.

The campaign uses two robotic test subjects: Atlas, a compact blue robot, and P-body, a taller orange robot. Unlike the single-player campaign, its puzzles are built around simultaneous actions, shared portals, timing, communication, and the need for each player to understand the other's position. The game supports online and local cooperative play on compatible platforms.

The Cooperative Testing Initiative is divided into themed testing courses, including Team Building, Mass and Velocity, Hard-Light Surfaces, Excursion Funnels, and Art Therapy. “Portal 2 co-op” and “Portal 2 Multiplayer” are understandable descriptions, but they are generic labels rather than the campaign's official in-game name. The robots' frequent deaths and GLaDOS's commentary are also deliberately part of its comedy.