So as some people know that Garry's Mod 12 will, or already has (for some) updated to version 13. I know there is people out there that don't want to update to GMod 13. So I have came up with a solution. Before the update, I saved the GMod 12 GCF File to another folder, and using GCFScape, extracted the "garrysmod" folder. I modified gameinfo.txt so that the name shows from "Garry's Mod" to "Garry's Mod 12". After installing Source SDK Base 2006 and 2007, I placed the "garrysmod" folder in C:/Program Files (x86)/Steam/steamapps/sourcemods and in an attempt to see if it worked. Amazingly it did! All GCF including, HL2, CS:S, and TF2 mounted natively, meaning, ragdolls, maps and textures are loaded correctly. Multiplayer might not work, I may be wrong, Hamachi VPN may serve as an alternative if that was the case. Addons (that are not written for GMod 13) should work the same. I don't have a 4shared file ready yet, but I will have one as soon as I can, hopefully by today, with the raw files. In the meantime, if GMod didn't update for you here's what you do. Get GCFScape: nemesis.thewavelength(dot)net/index.php?p=26 Locate the garrysmod content.cfg file. Open and extract ONLY the "garrysmod" folder. Install the folder to C:/Program Files (x86)/Steam/steamapps/sourcemods Install Source SDK Base 2006 and 2007 in steam. Restart Steam to see the changes. That's it, you will now have GMod 12 and 13 running side by side. I'll edit this post later once I have an upload ready. Edit: GMod updated to 13, and the sourcemod broke, so I'm figuring out how to run it without hl2.exe errors.