More than 12 terabytes of Steam-era data covering roughly 2003–2013 has leaked, according to The Verge and Engadget. Researchers say the archive spans essentially every title uploaded in that window and already surfaced assets tied to canceled Half-Life 2: Episode 3, cut Portal 2 content, and F-Stop — a Portal-universe prototype built around a camera mechanic.
Third-party digs include early Call of Duty and Resident Evil builds plus titles such as Mirror’s Edge, Batman: Arkham Asylum, and Dragon Age: Origins. Engadget notes reporting that a publicly reachable storage endpoint may explain why the haul stops around 2013, when Valve changed systems. Valve had not commented in early coverage. Legal and preservation angles both apply: historians get rare intermediate builds, while publishers face another massive unplanned disclosure of unreleased work.
Source: https://www.theverge.com/games/986552/12tb-steam-leak-half-life-2-episode-3