Office Insiders in the Slow ring can download the update via File > Account > Update Options > Update Now. This will bring Office to version 1612 (Build 7668.2048).
Here the full changelog from Microsoft as provided on their forums. There is no official blog post for the update available, in spite of some interesting feature additions.
- “View and restore changes in shared files: In Word, Excel, and PowerPoint, quickly view who has made changes in your shared documents, workbooks, and presentations, and easily restore earlier versions. To get started, click the Activity icon, which appears in the upper-right corner of any shared file stored on SharePoint, OneDrive for Business, or OneDrive. In the Activity pane, you can see who has edited your document recently, along with the versions they've created.
- Easily select and manipulate objects: In Excel, you can use the Surface pen when resizing, rotating, and moving handles on objects as well as us the pen button to Lasso select ink without visiting the ribbon.
- Closed captioning and multiple audio tracks: If a PowerPoint slide contains a video that has closed captions or multiple audio tracks, you can now play these tracks in your slideshow.
- New data transformation and connectivity enhancements: In Excel, the Percentage data type is now supported, and binary combining and function authoring experiences have been enhanced.
- Accessibility built right in: In Visio, we've improved support for using your keyboard, Narrator, and other assistive technology to work with shapes, edit with others, and more.
- Visio Viewer for iPad and iPhone: You can now view Visio diagrams on iPad and iPhone in high fidelity, in the office or in the field. Download the app here.”