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Valve's Cancelled Portal Prequel F-Stop Has Leaked

Kotaku • November 1, 2026 • technology

Key Points:

F-Stop, a cancelled 2007 prequel to Valve's Portal, has leaked online and is now fully playable thanks to combined leaks from multiple sources.
Originally developed during Valve's Directed Design Experiments, F-Stop featured gameplay involving an Aperture Science camera to manipulate perspectives and solve puzzles, but was scrapped after mixed playtester feedback.
Key assets for F-Stop surfaced in the massive Steam2 leak of Steam depot data, while the source code and map data were recently leaked via the Valve Cut Content project's Discord server.
The Valve Cut Content team verified the authenticity of the leaked files, which community members combined to reconstruct a nearly complete version of the game, estimated to be about 99% finished.
Although some minor assets and dialogue are missing, the leak provides a rare opportunity to experience a previously unreleased chapter of the Portal universe.

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