@the mighty atom
i have found something:
[quote]
Engine branch
Before starting a mod you need to choose which version of Source you will use. Change the SDK's engine version to the one you want.
Source 2006
Outdated - Original Half Life 2: Episode One mod. Only included for backwards compatibility reasons.
Source 2007
Original Orange Box mod. This is the most recent HL2-Based engine branch available. This is what most mods use!
Source 2009
Updated Orange Box mod. This is the current version of the engine with Mac support. However, you cannot make a mod for Source 2009; you can make a content-only mod of a 2009 game by following Creating a Mod manually.
Alien Swarm (via Alien Swarm SDK)
The oddball of the bunch. Alien Swarm is totally free to play and its SDK includes source code, but it's source code for a top-down shooter. It also lacks many of the HL2-compatible code's peripheral tools (including custom shader support) and cannot access HL2's content.
Source 2013
In 2013, Valve phased out the Source SDK with the release of SteamPipe. With this change, they updated the source code to the latest version of the Source-1-Engine for the HL2-based engine branch. This time around, the source code is not made available via an SDK launcher, but is instead hosted on Github. See Source SDK 2013 for more information.
Warning:Your Engine Version in the Source SDK must match the Engine branch of your mod! Failing to do this will result in Source SDK tools being unable to load required resources.
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