As a long-time Stardock customer, I had bought GalCiv 3 directly from Stardock, which is the Steam Version. My question is:

If I buy DLC's from GOG, will they be compatible with my Steam Version?

As GOG does not provide Keys for Installation i think it is not possible.

Thank you very much for your answers.

Does anyone know whether it is possible to exchange the steam-version for the GOG-version?

(hint to myself, wait until "Ashes" is released on GOG) ;)

I don't think it's possible. This question came up in the dev stream when GalCiv 3 got released here, and the answer was rather unfavourable. Still, you could ask Stardock support. Maybe they're willing to do it after all. It's already here. Unless you meant another game with Ashes in the title.

Thanks for pointing me to Ashes of Singularity, I hadn't noticed it on GOG. :)

I think it is great that Stardock now releases it's games directly to GOG as well.

I might ask Stardock if an exchange is possible. I prefer the GOG-Version due to their DRM-Free Offline installers (I keep a backup of my whole GOG-Collection locally) . It is not just GalCiv 3 but also SOSE Rebellion, the latter being one of my favorite games of all times. Although I don't think something is going to happen to Steam anytime soon, I don't trust it a 100% either, since I lost a couple of games when Impulse disappeared.