The Source engine should've died a decade ago, but Valve kept finding ways to keep it alive

A retrospective on Valve's Source engine, tracing its origins from a Quake-derived codebase in the late 1990s through its peak with Half-Life 2, CS:GO, and Titanfall, to its eventual succession by Source 2. The piece covers how Source introduced physics-driven gameplay, expressive NPC animation, and a robust modding pipeline that launched careers for developers like Garry Newman and Davey Wreden. Despite aging technical foundations, the engine was continuously extended — CS:GO's branch accumulated over a decade of upgrades, and Respawn built Titanfall on a heavily modified Portal 2 fork. Source 2 arrived gradually, powering Dota 2 Reborn (2015), Half-Life: Alyx, and finally Counter-Strike 2 (2023). The engine's lasting legacy is the generation of developers it trained and the design conventions it normalized across the industry.