A playable version of F-Stop, Valve’s canceled Portal prequel, has leaked online nearly 20 years after development ended. Leakers assembled the game from assets tied to Valve’s massive 12-terabyte leak in August, with missing source code and map data reportedly surfacing through the Valve Cut Content Discord this week.

Unlike the main Portal games, F-Stop replaced portals with a camera mechanic. Players photograph objects to capture them, then place them elsewhere using Polaroid-style images—an idea that feels similar to the later puzzle game Viewfinder.

F-Stop was created during Valve’s “Directed Design Experiments,” a three-month period in 2007 when the studio split into five teams to explore new game concepts. The project was short by design, with full playthrough videos of the leaked build coming in at under an hour.

Although Valve canceled the game, parts of its dialogue and ideas later appeared in Portal 2. The leaked version now offers fans the closest look yet at what the camera-based prequel might have become.

The reconstructed build is described as nearly complete, though it remains a fan-assembled project rather than an official Valve release. Its availability follows a wave of Valve-related leaks earlier this year that exposed large amounts of internal material.

For Portal fans, the leak is a rare chance to experience one of Valve’s most intriguing abandoned experiments. For Valve, it is another reminder that even projects canceled decades ago can resurface once their files escape into the public sphere.