Microsoft calls this build Windows Technical Preview and the build number is 9834 (Windows 8.1 is 9600), not Windows 9. So maybe it won’t be called Windows 9 after all?
There’s a video of it here: https://www.youtube.com/watch?v=--wgAsHWNRE#t=16
There’s also a review of the new features revealed in the video and a fair critique here: http://www.ghacks.net/2014/09/12/what-the-leaked-windows-9-screenshots-reveal-about-the-operating-system/?_m=3n%2e0038%2e1364%2ehj0ao01hy5%2e1eup
as well as here: http://www.neowin.net/news/windows-threshold-build-9834-screenshots-leak-shows-a-lot-of-new-features
I can’t say that these will be in the Technical preview, but it is likely that there won’t be big changes after it. That said, there are missing components likely to appear later, and that it appears that the animating tiles (in the video) can be irritating at times. Also, in the video, there’s no charms bar…but it’s referred to in the task bar and start menu properties, so it might very well still be a part of “Threshold”.
Anyway, just to keep you updated…
Sources: in the article links.