The game is free on Fanatical, although for a limited time, if you’re willing to jump through a few hoops. To claim it, you need to (1) create an account; (2) connect your Steam;* (3) verify your email address; and (4) sign up for their newsletter.

Good luck, and have fun!

P.S. Fanatical freebie keys tend to expire in ten days (from the start of this giveaway). However, there is no definite expiration date for this one. Either way, make sure to activate it as soon as possible. Also, after you’ve won, please leave feedback that you’ve received the key.

‎* Your Steam account must not be limited in that you have to have spent at least five US dollars within the Steam store.

Update
Congratulations to lidichi!