It’s FREE but there is a catch, it’s only FREE when you’ve signed up for the Gwent Beta. You can do that here.
Here is how to get the game for FREE: Download GOG Galaxy and do the following things in the client or the GOG website:
- Redeem the Gwent Beta Code.
- Go to the game page
- Refresh and now it should say FREE instead for the price!
It does work for me:
Otherwise you can also add the game to your cart although it says €9.99. People confirmed that it was free in the cart later on and they were still able to checkout.