Source 2013

The Source 2013 engine branch (also called SteamPipe branch) is the final iteration of the Orange Box engine branch. It was introduced by Valve in 2013 to replace the archaic GCF file format with the VPK format introduced in the Left 4 Dead engine branch. Major shifts in content mounting occurred, and all games using the Source 2009 and Source Multiplayer engine branches were upgraded to this version. Half-Life: Source was also upgraded to this engine branch from the Source 2006 engine branch. The "custom" folder was added to make modding easier and was added as a mounting path for each individual Source game.

While SteamPipe was praised for simplifying how the Source engine mounts content and including previously-unreleased Team Fortress 2 code, it also broke countless numbers of mods and worsened problems already present in the Source 2009 branch. It also does not have most of the features that the engine branches from the Left 4 Dead engine branch onwards had. However, the engine branch has been polished over time and is now the main branch in use by modern non-licensed engine mods.

Features

New since the Source 2009 engine branch is:

Linux support: The engine can now run on Linux. However, Linux support outside of official games may be spotty.
Prop lightmaps (only in ): Static props without bump maps can now use lightmaps.
Per-texel color tint masking for models: $blendtintbybasealpha is ported from the Left 4 Dead engine branch. Source 2013 includes an exclusive additional parameter, $blendtintcoloroverbase.