Another big win for 64-bit processors in general, Valve just announced support for 64-bit processors and OSs in their latest Source engine update. 
Bellevue, WA. — December 22, 2005 — Valve, a leading entertainment and technology studio, unveiled a 64-bit version of its Source game engine technology today. The first 64-bit Valve games released will be native 64-bit versions of Half-Life 2 and Lost Coast, and have been developed to take advantage of AMD Athlon™ 64 FX processor-based systems – the ultimate 64-bit gaming platform for PC enthusiasts.

The 64-bit versions of these games are being offered to all Half-Life 2 owners via Steam™, Valve’s online platform for delivering games and digital content directly to users around the world.