Which alternate reality game helped promote Portal 2?

The alternate reality game that helped promote Portal 2 was the Potato Sack. Valve launched it in April 2011 as a large, cross-game marketing event involving thirteen independent games.

Players searched for hidden clues, images, achievements, and Portal-themed updates across the participating titles. The campaign presented itself as an effort to reboot GLaDOS, Portal’s artificial-intelligence antagonist, and encouraged players to coordinate their discoveries through online communities. The potato theme also echoed Portal 2’s story, in which GLaDOS is temporarily powered by a potato battery.

The Potato Sack was both the name of the ARG and the discounted Steam bundle containing the participating games. Completing activities across those games helped fill a shared progress meter associated with “GLaDOS@Home.” When the community reached the required target, Portal 2 became available roughly ten hours before its planned release window on April 19, 2011.

A common mix-up is confusing this event with Portal’s earlier ARG, which used cryptic clues connected to the first game. The Potato Sack was the later, much larger campaign specifically tied to Portal 2’s launch.