Xbox Live Gold and PS Plus are unfortunately needed
As much as I just could not click with Steep enough to want to get drawn into another open-world setting and all that entails, I get the game's appeal. I also believe it's a particularly good match for the free-weekend treatment. You get in, you hopefully have a good time, and you get out. Done and done. If you think so too, know that the event is now live on PC, PlayStation 4, and Xbox One.
From now through March 12 at 11:59pm Pacific on Xbox One and March 13 at 10:00am Pacific on PC and PS4, the "entire" game is playable at no extra cost. But -- why is there always a but? -- you will need a PlayStation Plus or Xbox Live Gold subscription to take part in the console versions.
Size-wise, you're looking at around 17GB to 25GB, depending on the platform.
Play Steep for Free From March 10-12 [Ubisoft]