Buy at Frictional Games and download from Steam

[Ace]

Hi guys

I want to buy this game but i have some unanswered questions.

I want to be able to play the game on both linux and windows. Thats why I will buy it from Frictional Games. But when i am on windows i want to be able to use steam. (When the linux client is released i will use only steam)

To use steam i need a CD-Key. After the purchase will i become a key or just able to download from store?

And thanks for this cool game. We need good games like Amnesia!