Where Do I apply to the Development build?

[PinkPWNY 10]

I was just wondering where to get the Development build because a bunch of my friends are playing it?

[5133p39 12]

Right click on "Arma 3 Beta" in your Steam games library, select "Properties", click on "BETAS" tab, change the first field from "NONE - opt out of all beta programs" to "development - Development build"