'GMod 13 is kind of like pulling a plaster off fast, all in one go,' he told me. I asked Garry to walk me through the most important future updates. The base game will be better, but other things will break. Firstly, it gives Garry the opportunity to make big changes without constantly dealing with complaints that the game is broken, and secondly, it gives everyone a look at what's being done to prepare for when the release arrives. It uncouples the development from the main fork, and that serves two purposes. The beta, aka GMod 13, is a relatively recent arrival, built to allow Garry to overhaul the whole game without breaking the one everyone's playing.
There are two versions of Garry's Mod: the standard version that's been in the same shape for a while now, and the beta.