For those unfamiliar with Black Mesa, it’s essentially a third-party remake of Half-Life (1998), developed and published by Crowbar Collective. It received a standalone commercial release through Steam Early Access on May 5, 2015, with a full release slated for Q2 2019. In this game, the player controls Gordon Freeman, but unlike the original game, this one includes an entirely reskinned collection of textures, models, and NPCs, a noticeably longer runtime, and additional dialogue and story elements. Read more for two gameplay videos and additional information on how to play these new levels.
“To take part in the beta, find Black Mesa in your Steam library (you’ll need to own it, and if you don’t it’s currently on sale) and right-click on it. Select Properties from the drop-down menu, then choose the beta tab. Opt-in to the public beta and close the menu. You’ll see Black Mesa updating to provide you with the Xen chapters. When you launch the game, you can select New Game and choose chapter 15 to start playing the Xen beta,” reports PC Gamer.