Microsoft announced its plans for Office 2016 back in January, and then released a preview version including Word, Excel and PowerPoint for Windows 10 testers. Now the full suite is available as a beta preview for IT pros and developers.
The beta can be accessed via Microsoft's Connect program. You'll have to fill out a form and see if you qualify -- only customers who already have an Office 365 Business plan are eligible.
That means the Windows 10 version is easier to access, but it doesn't include the full platform. In particular, the IT pro/developer preview has Outlook, which is being enhanced significantly with a new sync protocol and support for multi-factor authentication.
Hit the Microsoft announcement post below for full details of the server-side enhancements coming to Office. There's also still no word on a final release date, beyond the previously stated "before the end of 2015".
Announcing the Office 2016 IT Pro and Developer Preview [Office Blogs]