I've bought The Witcher 3 on GOG. I'm wondering if I'll be able to use my GOG copy to unlock the game on steam.

They are not planning on offering a backup copy on GOG for the games bought on Steam, so I would think that Steam would not offer a backup copy either.

No.

No, GOG almost never offers Steam keys with their purchases.

If you had bought it on Steam, you might have gotten a GOG Backup somewhere after release (since GOG is owned by the people who made the Witcher, and they offered backups for 1 and 2 in the past), in the same way that a lot of games on Steam you can activate on Origin (EA games)

Must... resist... message of... devas... tating... snark... aaaaaaaaaaaah...

No. Why would you want that anyway?

To still have access to Steam while I play, steam achievements, have it in my library, etc...

Not to mention I have save games for Witcher 1 and 2 on Steam, and I want to be able to import them into Witcher 3

That doesn't work if you just activate the game on Steam?

You can use your keys of Witcher 1 & 2 from Steam to get the games on GoG from this link, but they are not going to go from GOG to Steam unfortunately.

Well, apart from the save games these aren't really desirable things. I'm sure someone can help you import them though! Maybe on the Witcher 3 forums. I dunno.

For you maybe. I like seeing how many hours I've played, unlocking achievements, and being able to chat in game with friends. I suppose I can get all those besides achievements, but still.

I'm sure save games between GOG and Steam share the same format too, so I might still be able to import them.

This forum is filled with people like that.

"I don't like these things and you shouldn't either."

As for the saves, I don't see why you wouldn't be able to use them on both GOG and Steam.

I bet they should transfer save games. I was referring to the game key from here not working on Steam. I have 1 & 2 on both gog and Steam and next time I try to transfer a game I'll let you know if it works if you want.

If it helps any Witcher 3 will no doubt have some integration with the GOG Galaxy Client so Hours played and Achievements might be present there already. Although I doubt many of your friends will be using the Galaxy client unless they all happen to be playing Witcher at the time.