Very good news today! After many months of preparation, KSP is now available on Steam!
We're very fortunate also in that we're one of the very first games to be released as a Steam Early Access title. We've been working closely with Valve recently to make sure the release went as smoothly as possible, and their new Early Access category is just perfect for us. We're all very happy here!
So, I think we should probably have a little Q&A here, to clear up what'll likely be the most frequent questions:
Q: If I've already bought the game on the KSPStore, can I switch over to Steam?
A: The answer to that is Yes, but not right now. We are going to set up a system on our store where you'll be able to get a Steam key for KSP provided you already have purchased the game. However, we are still working on the exact details of this feature, so it'll likely be a while until that's set up. We'll of course let you know when that becomes available.
Q: What platforms are supported on the Steam version?
A: KSP is available on Steam for all three platforms (Win, Mac and Linux), and the Demo is also available on all of them as well.
Q: What is this Early Access thing you speak of?
A: I think Valve can explain it better than we can.
Q: Is this in any way related to the 0.19 update being smaller than usual?
A: You've probably figured out already this is one of the main reasons we cut the 0.19 update short. We wanted KSP to look its best for the release, so we decided to get the reentry fx, animations and all the other features out in time for it. The shorter update cycle worked out nicely for us though, so we'll try to maintain that flow for future releases as much as possible. The patcher should also be ready by then.
Q: Speaking of patcher then, how does that work with Steam?
A: Steam has its own update system, so for the steam version of the game, we've turned off all version-tracking features in KSP. The Steam version will update automatically when we publish new builds, so it all happens without the need of any external tools. The patcher will only be used for the KSPStore-bought version of the game.
That's all I can think of for now. If other relevant questions pop up in the comments, I'll update this post here to include an answer to it.