Content complements of: https://wordpress.org/news/2015/10/wordpress-4-4-beta-1/
WordPress 4.4 Beta 1 is now available!
This software is still in development, so we don’t recommend you run it on a production site. Consider setting up a test site just to play with the new version. To test WordPress 4.4, try the WordPress Beta Tester plugin (you’ll want “bleeding edge nightlies”). Or you can download the beta here (zip).
WordPress 4.4 is slated for release on December 8, but to get there, we need your help testing what we have been working on, including:
Twenty Sixteen — The newest default theme for WordPress.
Responsive Images — WordPress automatically delivers a more appropriate image to users depending on a variety of conditions like screen size, viewport size, and screen resolution.
Embeds — WordPress can now embed rich content from nearly all sites that support the oEmbed standard — not just YouTube, Flickr, Twitter, and the like. You can even embed previews of posts from other WordPress sites by pasting the URL on its own line.
There have been a lot of changes for developers to play with as well:
REST API (phase 1) — The underlying infrastructure of the WordPress REST API plugin has been included in WordPress 4.4. Plugin authors can take advantage of this by adding custom endpoints.
Term Metadata — Taxonomy term metadata is now included in WordPress 4.4. If you’ve already been using a plugin to implement term metadata, you should read this post on how to prepare. Also, the underlying WP_Term class improves caching when working with terms. (#14162)
Improved <title> output — wp_title() is now deprecated; WordPress can handle the rendering of the document title automatically.
Comments — Comment queries are now split for performance. Also, the underlying WP_Comment class improves caching and introduces strong-typing. (#8071, #32619)
If you want a more in-depth view of what major changes have made it into 4.4, check out all 4.4-tagged posts on the main development blog, or check out a list of everything that’s changed.
If you think you’ve found a bug, you can post to the Alpha/Beta area in the support forums. We’d love to hear from you! If you’re comfortable writing a reproducible bug report, file one on the WordPress Trac. There, you can also find a list of known bugs.
Many small changes
Some groundbreaking new features
Fun times had by all