https://www.pcgamer.com/play-fallout-4-for-free-this-weekend/

If you've been waiting for just the right moment to finally dive into Fallout 4, it's here. Fallout 4 is free to play on PC right now, and this free period lasts until Sunday, February 4. During that time, the base game is 50% off (Steam says this 'weekend deal' lasts until February 12, which may either be an error or an exceptionally long weekend).

Other discounts during the free weekend: 40% off Fallout 4 Game of the Year Edition (which includes all the DLC) and 50% off the season pass. Here's the full list of discounts: