Fallout 4 is free to play all weekend for XBox One Gold members and Steam users. From Thursday, May 25th through Sunday, May 28th, anyone can try out the full base game as well as enjoy full mod support. Download of the client begins Thursday at 12:01 am Pacific / 3:01 am Eastern (that's tonight!) on XBox Live with the game open after the download is complete. Steam users can access the free trial starting at 10:00 am Pacific / 1:00 pm Eastern tomorrow.
The best part is that anyone interested in purchasing Fallout 4 can do so with a whopping 67% discount throughout the weekend.
Check out the full announcement on the Fallout 4 blog on the Bethesda site.