Massive 12TB Steam leak reveals decades of unreleased games — archived files include unseen Half-Life 2: Episode 3 builds and assets

Valve might've just suffered its biggest data leak in history, but it wasn't a hack or a security breach. Instead, the company left an endpoint to its legacy infrastructure accessible to the public, from where archivists extracted 12-13TB of old game content. The files are still being explored, but we know they include both Valve's internal projects and third-party releases, with an early weapon asset from Half-Life 2 Episode 3 being the key discovery, along with scrapped Portal 2 concepts.

The archive consists of old Steam content-server data from 2003 to 2013, overlapping with the timeline of the platform's upgrade from the old Steam2 system to SteamPipe. Valve used to distribute games via proprietary NCF (No-Cache File) and GCF (Grid Cache File) formats during the Steam2 era before it transitioned to a standard HTTP file-tree system around March 2013. Therefore, this dump basically acts like a preserved time capsule.

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During this period, Valve was a much more active game developer, so we get a rare insight into their projects. First up is Left 4 Dead, and the files include an entire early build of the game from June 2008. It has a different HUD, different voice lines cut from the retail release, altered sections of the map, and many unfinished early assets that Valve was recycling from the Terror Strike mod (for Counter-Strike: Condition Zero).

Then, there's Portal 2, which is actually said to have been hit the hardest, and modders have similarly reconstructed a playable build from the files. It's a beta dating back to July 2009 when the game was still in its Core Hub era before that concept was scrapped in favor of a more direct sequel. We also get to see early assets from the F-Stop prequel that was in development the year prior, featuring camera mechanics for gameplay.

An intro sequence shows the player falling down one of the labs. The beta features a completely different GLaDOS, with a more passive role, different voice lines, and new animations. Some of the scenes in this build are so unfinished that they use assets from Team Fortress and Half-Life as placeholders. But perhaps the most exciting discovery here was a 3D weapon model for "Weaponizer."

Weaponizer is supposedly a concept weapon from the canceled third episode of Half-Life 2. It's been leaked for years and officially shown off by Valve, too, but never in a build form. It's used to turn objects into ammo, but Valve was using it as a placeholder for a handheld Paint Gun before switching to gel drops. Still, the fact that it exists in this early build of Portal 2 just goes to show how close we were to getting Episode 3.

Finally, we got a decent look at CS:GO as well, which looked much more like Source in its early development days, with a more stylized UI and alpha versions of maps. There was an MP5-Active weapon found in the files, suggesting it was part of the original launch roster at some point, along with a bunch of early knife models, cut grenade mechanics, and a Riot Shield brought back from Counter-Strike 1.6.

The archive also includes builds from 2011 that run on Source physics and movement but feature early Left 4 Dead 2 engine code and prototype CS:GO UI elements. This was right around the time CS: GO was born as a whole because, up until then, Valve was simply trying to port Source to home consoles. The extensive upgrades made by Hidden Path Entertainment convinced the company to release a new Counter-Strike game entirely.

Those are just a few tidbits from the giant dump that's sure to dish out more information over the coming days. Someone found an early beta build of Sonic 4 Episode 2 in the files, so expect to see more from third-party games as well. Valve has not acknowledged the leak so far, but given that even the latest "leak" in this archive is over 13 years old, it's probably not a major internal concern. Besides, all this data was only discovered because of a mistake on Valve's part, not a breach.

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