A playable build of F-Stop, a cancelled Portal prequel developed by Valve, has been made available by modders and leakers following a large data leak. The game, previously a mysterious "white whale" for fans of the Portal and Half-Life series, features a core mechanic where players photograph objects to make them disappear, and can then use those photos to reintroduce the objects, potentially altering their scale.
This F-Stop concept was first detailed in a semi-official capacity in 2020, drawing comparisons to the puzzle game Superliminal. While Valve head Gabe Newell reportedly favored early versions of the game, it did not perform well in testing. Elements of F-Stop were later incorporated into Portal 2.
The ability to play F-Stop now stems from a significant leak of 12TB of Steam data in August, which initially only contained game assets. Source code and map data for F-Stop were later shared by someone who reportedly requested $1000 before releasing the files. Modders within the Valve Cut Content Discord server were instrumental in assembling these leaked components into a functional game.