F-Stop Leak Makes Canceled Portal Prequel Playable, Reportedly 99% Complete, Nearly 20 Years On

The F-Stop leak has turned one of Valve’s best-known lost projects into something people can actually play. Nearly two decades after the company shelved its camera-based Portal prequel, leakers and members of the Valve Cut Content community have assembled a version that is reportedly almost complete.

Both The Verge and Kotaku reported the news on November 1, 2026. Their accounts agree on the main points, though they differ slightly on some details.

What F-Stop was supposed to be

F-Stop came out of a short, unusual stretch at Valve in 2007. Over about three months, which Gabe Newell would later call the Directed Design Experiments, the studio split into five teams. Each built a rough prototype of a new idea, and F-Stop was the fifth.

It was conceived as a prequel to Portal. Instead of a portal gun, players used an experimental Aperture Science camera. Photographing an object captured it, and the resulting Polaroid-style picture could be used to place that object somewhere else. The Verge likens the idea to the more recent puzzle game Viewfinder. Kotaku describes the core of the game as manipulating perspective to solve puzzles.

Newell was reportedly very taken with the concept, but playtesters were less impressed, and the project was dropped. Pieces of it survived. Some dialogue, characters and mechanics were reworked into Portal 2.

How three leaks became one playable game

The F-Stop leak is not a single event. It is the result of three separate leaks being stitched together.

The first was a huge dump of Steam depot data in late August, which Kotaku says was dubbed “Steam2.” The Verge puts its size at 12 terabytes and Kotaku at roughly 13, so the exact figure is unclear. It reportedly covered nearly every Steam depot from 2003 to 2013, and, surprisingly, most of F-Stop’s assets. But it lacked two key ingredients: the game’s source code and its mapsrc data, which is Valve’s name for the folder holding map source files.

Those final pieces reportedly appeared this week on the Valve Cut Content Discord server. Kotaku says they arrived over roughly 48 hours. It also reports, citing the server’s moderators, that the person behind the map data first asked for $1,000 but ended up releasing it for free. Kotaku adds that the Valve Cut Content team verified the map files as authentic before the community combined everything into a working build.

How complete is it?

According to Kotaku, players say a few assets and dialogue lines are missing but that the game is essentially 99 percent complete. That figure comes from player reports, not an official assessment, and Valve has not commented in either source.

It is also short. The Verge notes that videos of the full campaign all run under an hour, which fits a prototype made in a three-month window. Anyone expecting a full-length Portal game should adjust their hopes. What the build offers is a look at an unreleased experiment and how an idea was tested before being folded into a better-known sequel.

Why the F-Stop leak matters

For fans of Valve’s history, the significance is that F-Stop is no longer lost media. Until now it was known mostly from developer anecdotes, the Half-Life wiki and scraps of surviving material. People can now see how the camera mechanic worked in practice and judge for themselves why playtesters were lukewarm.

It also shows how much of Valve’s past has come to light this year. The August Steam2 dump supplied the raw material, and community preservation groups did the work of verifying and assembling it. Whether Valve responds is unknown, since neither report includes any statement from the company. For now, the F-Stop leak means a game that was 0 percent available a week ago can be played from start to finish.

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