Update : Windows 10

[Mudbill]

If you buy it right now... I'm unsure. I suspect Microsoft has already shipped it to manufacturers, but I don't believe they're allowed to sell them before the release date. So most likely you'll get 8.1. If you wait until sometime after the release on the 29th, it might come pre-installed. To be safe (if you mind, that is), I'd wait a bit more just to make sure the ones with 8.1 are done away with before buying, if you aim for it to have 10 already.