Leakers have pieced together a playable version of F-Stop, a canceled Portal prequel, according to The Verge. Most of the assets came from a 12-terabyte leak in August. The source code and map data were not part of that leak. The report says those final pieces reached the Valve Cut Content Discord this week, which allowed a nearly complete version to be assembled.
The game centers on a camera mechanic. Players capture an item by taking its picture, then place it elsewhere using the resulting Polaroid-like photos. The Verge compares it to Viewfinder in that respect. Some dialogue and elements from F-Stop later appeared in Portal 2, the report says.
According to the report, videos of the full campaign each run under an hour. The Verge links this length to the game's origins. F-Stop was developed during the "Directed Design Experiments," a three-month period in 2007 when Valve split into five teams to build experimental games.