13TB Steam Leak Reveals Valve Prototypes, Scrapped Portal 2 Mechanics

On August 29, approximately 13 terabytes of Steam depot data became publicly available. This leak is being called the largest video game-related leak on record, containing prototype builds from thousands of games spanning both Valve’s own releases and third-party titles. The leaked depot files date from 2003 to 2013, a span that covers some of the most pivotal years in modern gaming history.

The Half-Life Disappointment and the Weaponizer Discovery

No playable build of Half-Life 3 or Half-Life 2: Episode 3 has emerged from the leaked data, disappointing those who hoped for evidence of Valve’s long-rumored sequel and expansion. However, Half-Life 2: Episode 3 is not entirely absent from the leak.

The most significant Half-Life discovery is a model for the Episode 3 “weaponizer” gun. This is particularly noteworthy because the community has been aware of this weapon’s existence since 2011, when filenames referencing it leaked alongside mentions of an “ice gun” and “flamethrower.” The discovery gained new context in 2024 when Valve released the Half-Life 2: 20th Anniversary Documentary, which featured brief footage showing weapons intended for Episode 3, including the ice gun and what the community believes is the weaponizer.

The model itself appears in a Portal 2 prototype build, suggesting it may have served as a placeholder for a scrapped painting tool. Unconfirmed reports also indicate filenames appearing in an “ep3” depot, though these should be treated with skepticism for now.

Portal 2: The Leak’s Centerpiece

Read also: Fall Game Season Launches With Onimusha, Tactics, and Indie Adventures · Naughty Dog Wraps Motion Capture for Intergalactic as 2027 Launch Looms · Pokémon World Championships Struggles With Lottery Demand

The 2009 Prototype Build

At least two distinct Portal 2 prototype builds feature in the leak, making this the most substantial discovery so far. The 2009 build offers a rough glimpse into the game’s early development, with rough concept versions of unfinished cutscenes and placeholder models. The early intro sequence shows Portal 2 in a much earlier stage, before many of the polished elements that made the final version memorable.

Among the curiosities found in this build are placeholder visual elements, such as a random rat that appears when opening a specific door. More intriguing is a cut line of dialogue in which GLaDOS refers to itself as Chell’s “mother,” a characterization that never made it to the released game.

The 2010 Build and Three Scrapped Mechanics

The 2010 prototype build is where the truly fascinating discoveries lie. This version contains working, though incomplete, implementations of three gameplay mechanics that were ultimately removed: Adhesive Gel, the Paint Gun, and a slow-motion mechanic resembling bullet-time.

Adhesive Gel and the Paint Gun were not entirely unknown to the community—Portal 2’s developer commentary mode included discussions of both features. However, this leak provides the first opportunity to actually see them in functioning form within the game engine. The Adhesive Gel mechanic allows the player to walk on walls by adhering to them, a feature that developers apparently found visually interesting enough to justify extended development before cutting it.

The slow-motion mechanic also appears fully realized, with sound effects intentionally slowed when activated. These elements suggest that Valve invested considerable effort in mechanics that ultimately did not align with the final game’s design direction.

Counter-Strike: Global Offensive’s Aborted Console Versions

Multiple Counter-Strike: Global Offensive prototype builds have been identified, with at least three separate versions discovered. These builds contain evidence of console development, most notably in the form of PlayStation 3 and Xbox 360 button prompts, indicating that Valve at one point pursued ports to those platforms. The builds also contain scrapped character models, including an unused female character model.

A notably polished but unused version of the game’s heads-up display has also surfaced, complete with weapon animations that never appeared in the released version. Among the more unusual discoveries is the inclusion of “Family Guy ragdoll physics,” a curious placeholder that adds an element of absurdist humor to the discovery.

Perhaps the most interesting aspect for Counter-Strike veterans is the presence of scrapped maps. Some of these maps appear to draw inspiration from locations in the original Left 4 Dead, though they function as recreations rather than direct copies. It remains unclear why Valve chose to discard these maps, particularly given how extensively Counter-Strike players gravitate toward familiar classics like de_dust.

Left 4 Dead 2’s Rough Prototypes

At least two Left 4 Dead 2 prototype builds are present in the leak, though they reportedly contain numerous bugs and crash at specific points within certain levels. The discoveries here are less dramatic than those surrounding Portal 2 or Counter-Strike, but still contain notable curiosities.

The prototypes feature higher jump values than the final release, suggesting Valve experimented with more mobile character movement. Additionally, the Dark Carnival level’s concert section contains placeholder audio that has drawn amusement from those who have heard it. More interestingly, the majority of Left 4 Dead’s maps are included in the Left 4 Dead 2 prototypes, indicating they were likely retained for testing purposes to verify that Left 4 Dead 2 could properly run the previous game’s maps.

F-Stop: The Portal Game That Never Was

Gabe Newell’s 2007 Design Experiments

F-Stop is a canceled project from 2007 that represents one of gaming’s great “what-ifs.” Gabe Newell initiated what he called the “Directed Design Experiments,” during which Valve’s team spent three months prototyping five entirely different game concepts. F-Stop was one of these experiments, conceived as a prequel to Portal.

The core mechanic involved taking photographs and then scaling them in unconventional ways to solve environmental puzzles—a concept not unlike the later indie game Superliminal. According to Newell, the team found the concept compelling enough to warrant full development, but the project was ultimately shelved in favor of Portal 2.

F-Stop Assets and the Cave Johnson Revelation

Although no standalone F-Stop prototype appears in the leak, several F-Stop assets have been discovered within Portal 2’s prototype builds. This aligns with Newell’s previous statements that F-Stop’s brief development influenced some of Portal 2’s puzzle design and that assets from the canceled project were recycled for testing purposes.

The most substantial F-Stop discovery is a nearly 10-minute placeholder recording of Cave Johnson dialogue intended for F-Stop, not Portal 2. In the recording, Cave Johnson instructs the player to retrieve the “Aperture Science Spirit Camera” and take photographs—specifically of what he describes as his “big old butt.” This dialogue was voiced by J.K. Simmons, the actor who provided Cave Johnson’s voice throughout the Portal series. The existence of this recorded material provides a tangible window into what a fully developed F-Stop might have felt like, right down to the irreverent character work that defined the Portal franchise.