Today, Microsoft is releasing a new build of Office 2016 for Insiders, bringing the version number to 1801 and the build number to 8911.2016. The version number indicates that this should be generally available to everyone in January.
While new apps are available for Word, PowerPoint, and Outlook, the biggest changes arrive in Excel. One of those is Excel Insights, which uses machine learning to help "identify trends, outliers, and other useful visualizations." To use it, click on a cell and go to Insert -> Insights.
Excel Insights are rolling out gradually to Insiders, so you might not see it right away.
Another new feature is the ability to deselect a selection. You can now deselect cells by pressing the Ctrl key and using the Deselect Tool.
In all of the Office 2016 apps, you'll find that the version and build numbers are in a different location. They're now next to the About button under File -> Account. Obviously, this won't change anyone's user experience, but it's part of the changelog.
Finally, Outlook 2016 includes improvements to groups, and conversations "load faster than ever".
In order to get the latest Office Insider build, you'll need to be an Office 365 subscriber. You can either download the Insider build directly from Office.com, or you can change your settings under File -> Account.