Portal F-Stop Leak Makes Valve’s Cancelled Prequel Playable

Portal F-Stop, the Portal prequel Valve cancelled in 2007, can now be played from start to almost finish. Fans combined three separate leaks this week into a build that players describe as about 99% complete, with only a few missing textures and dialogue lines. Valve has not commented and has never announced plans to release the game.

The final pieces arrived on October 31, when map source files for the game appeared online. The Valve news and leaks account Gabe Follower summed it up in a widely shared post:

There was another Valve leak. Someone shared maps from F-Stop, the canceled Portal sequel. Compiled with all the previous leaks, F-Stop is fully playable with all code, assets, and now maps available to the public.

— Gabe Follower (@gabefollower) October 31, 2026

How the Portal F-Stop Leak Came Together

The playable build is stitched together from three leaks. The first was the roughly 12 to 13 TB dump of old Steam depot data that surfaced in late August, often called the Steam2 leak, which we covered when the massive Valve leak revealed unreleased Half-Life and Portal assets. It held most of F-Stop’s art and sound, but not its code or maps.

Over the past few days, the source code and the “mapsrc” folder, Valve’s name for its map source data, were posted to the Discord server of the Valve Cut Content project. According to Kotaku, moderators there said the person holding the map files first asked for $1,000, then shared them for free. The Valve Cut Content team says it has checked that the map files are authentic.

What Was F-Stop?

F-Stop came out of a three-month internal exercise in 2007 that Gabe Newell later called the Directed Design Experiments, in which Valve split into five small teams to prototype new ideas. F-Stop was the fifth, a prequel to Portal built around an experimental Aperture Science camera.

The core mechanic works like this: you take a photo of an object, the object disappears into the picture, and you can place it back into the world later, sometimes at a different size, to solve puzzles. Fans have compared it to the 2019 indie game Superliminal. Newell reportedly liked the prototype, but it did not test well, so Valve shelved it and reused some of its characters, dialogue and ideas in Portal 2.

A first detailed look at the concept emerged in early 2020, and Engadget notes that YouTube playthroughs of the new build look largely stable despite the gaps.

What It Means for Players

This is not an official release, and it is built from leaked Valve code and data, so Valve could act against copies that circulate. For now it is the closest look anyone outside Valve has had at one of its best-known unfinished projects, at a time when fans are also tracking reports about Valve’s HLX project, widely believed to be Half-Life 3.