Goed nieuws voor alle modmakers onder ons, want Eric Johnson van Valve heeft laten weten dat de Source engine System Developing Kit eerder zal verschijnen dan Half-Life 2. Op deze manier kunnen mappers en modders alvast hun werk doen voordat het spel in de winkels ligt. Er gaat tevens een gerucht dat het Day of Defeat team al werkt met Source, hoewel dit ontkend werd door Johnson die liet weten dat het team bezig is met versie 1.1.Erik says: "Yes, we will be releasing an SDK for the Source engine for MOD developers before the game is shipped."

Considering the SDK for the original Half-Life wasn't ready until months after the game's release, this is great news!

The physics in the single player part (judging from the movies from E3) look absolutely fantastic, but how will physics work in multiplayer? Won't there be a problem with sending all the physics information packets to all the players? Are you perhaps scaling the physics engine down for multiplayer?

Gabe Newell: Well, the simple answer is that there are client-side and server-side physics behaviors. You use client-side when maintaining cross-client coherence isn't important. This cuts down network traffice while maintaining the appearance of physical simulation throughout the world... it's definable per-object, so exactly what's client vs. server simulated is tunable." En er is meer Half-Life 2 nieuws, want in deze post wordt gesproken over de physics in de multiplayer kant van Half-Life 2.