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The official site for Cuphead says that this is cross buy, and you can purchase it once and play on both PC and Xbox One. Does that apply to the GoG version as well, or do we only get half the package for the same price?
No, I'm pretty sure this applies to the Microsoft store exclusively. Neither the GOG nor the Steam version are connected in any way to your Microsoft account.

The official site says: Buy on GOG, buy on Steam OR buy on Xbox One & Win10 (via Microsoft store).
Post edited November 25, 2017 by colorito