Later this month, Microsoft is expected to release a public build of Windows Threshold for use by developers and enthusiasts alike. But, if you are a top tier Microsoft partner, there is a good chance that you already have access to these builds.
It was tipped to Neowin a few weeks back that partners were starting to get more recent builds of Threshold and we have been able to confirm that this is true. But, if you are thinking that this will mean a leak soon, don't get too excited as there are many security features in place to discourage these groups from letting anyone see the contents. On top of this, not all features are enabled in these builds.
Microsoft has always worked closely with its key partners, so it is not a surprise to hear this, as they need to keep these groups informed about the company's direction.
Windows Threshold will introduce a number of new features that you can read about here, most notably, the return of the Start menu. It is expected that Windows Threshold will likely be called Windows 9 to help push Microsoft past the woes that Windows 8 has introduced. Of course, naming is subject to change but by all accounts, this is a large update for Windows.
As we get closer to the rumored release date, expect that more information will get leaked as more users get their hands on Microsoft's latest builds.