SQL Server 2016 RC 3 is the last of our publicly-available release candidates. You can try this in your development and test environments, and it is available for download today.
In SQL Server 2016 RC 3, enhancements consisted primarily of bug fixes. We continue to refine the product for general availability. For the current release notes, see SQL Server 2016 Release Notes.
That “last of our publicly-available release candidates” thing says to me that we’re going to see RTM soon.