A massive 12-terabyte cache of apparent internal Valve data began circulating online on 29 August, containing builds and assets from titles including Portal 2, Left 4 Dead and Counter-Strike: Global Offensive, as well as material from the cancelled Portal follow-up F-Stop and files potentially linked to the long-abandoned Half-Life 2: Episode 3. The leak matters because Half-Life 3 and Episode 3 have become gaming's most notorious vapourware, and this is the most substantial trove of related material to surface since Valve's 2003 Half-Life 2 source code theft.

The material appears to span around a decade of development, ruling out any connection to the 2003 breach, and its origin and the identity of whoever obtained it remain unknown, with researchers expecting the full contents to take weeks to catalogue. The strongest Episode 3 lead is a "Weaponizer" object, previously referenced in a 2011 Dota 2 beta leak and shown in unseen 2024 footage, which dataminer Gabe Follower says has now turned up in the new files, though Valve's habit of reusing assets means it could originate from Portal 2 instead. The Portal-related finds are more concrete, including a playable July 2009 Portal 2 development build and assets from F-Stop, an experimental photography-based successor to Portal that Valve ultimately scrapped in favour of a more conventional sequel.