Why Garry's Mod 64 bit? Although it is a dev-branch/beta of GMOD, it dramatically increases performance of the game. I do not have technical specs of how much it increases performance, but I myself could clearly tell a difference when changing to it. It also allows for use of in-game web, such as the Cinema or Televisions in-game to watch YouTube videos (AKA It supports HTML 5). How to get Garry's Mod 64 bit > Open Steam Client > Go to Library > Right click Garry's Mod > Click Properties > On the top tabs, select Betas > In the top drop-down, select " x86-64 - Testing 64-bit builds " > Let Garry's Mod update This branch regularly gets updates as it is a work in progress still. If for whatever reason you no longer wish to use Garry's Mod 64 bit, you can change back to the normal branch by doing the above sequence but select " NONE - Opt out of all beta programs " in the beta drop down. Your game will update and return to regular GMOD.