12TB Archive of Old Steam Leaks Online, Revealing Portal 2 Prototypes, Early CS:GO, and Episode Three Traces

A massive dataset of around 12TB has surfaced online, containing working files and game depots from Steam‘s early content delivery infrastructure spanning from 2003 to 2013. Dataminers have already discovered dozens of unreleased builds in the archive: prototypes of Portal 2, assets from the canceled F-Stop concept, an early build of CS:GO, source code for Left 4 Dead, and even assets from the canceled Half-Life 2: Episode Three.

Early CS:GO on Source Code and Portal 2 Prototypes

As reported by tech publication VideoCardz, the archive marks one of the largest leaks in the history of the Source engine. Valve project researcher Gabe Follower reported discovering one of the earliest builds of Counter-Strike: Global Offensive, which at that stage was essentially a deep modification of Counter-Strike: Source.

A huge portion of the data centers on the development of Portal 2:

• the dump includes interim builds from 2009–2010;
• textures and mechanics were found for the canceled F-Stop project—an experimental game without portals that Valve originally worked on as a sequel to the first game;
• draft versions of Left 4 Dead maps from early behind-the-scenes E3 presentations were uncovered.

According to Spilled, enthusiasts have only just begun cataloging hundreds of gigabytes of compressed assets, so the list of discoveries will likely grow.

Episode Three Artifacts and Archive Scope

The most intriguing discovery is references to the unreleased Half-Life 2: Episode Three. The files contain a 3D model of the Weaponizer device, which appeared in early concepts for the continuation of Gordon Freeman’s story. However, there is no playable build of Episode Three in the leak.

Dataminers emphasize that the archive ends in 2013, making it pointless to look for leaks regarding modern or unannounced Half-Life 3 projects—the files solely reflect an era from a decade ago.

Not Just Valve: Thousands of Third-Party Projects

The leak is not limited to internal projects from Gabe Newell’s studio. The dump covers the old Steam2 system, which was used to distribute digital releases from third-party publishers:

• early PC builds of the platformer Sonic the Hedgehog 4: Episode II were found;
• interim assets for Fallout: New Vegas;
• thousands of archives containing patches and assets from dozens of indie and major studios of that era.

No Hack Involved: Technical Reason Behind the Leak

According to researchers, the incident was not the result of a hack into Valve’s internal network. The data was downloaded via a forgotten public endpoint on legacy Steam2 content delivery servers, which remained accessible due to a permissions misconfiguration.

The archive’s 2013 cutoff is tied to the platform’s history: that year, Valve announced on community forums a global migration of all games from legacy GCF containers to the modern SteamPipe file architecture (VPK format), after which the old repositories were archived.