After much anticipation, Preview 1 of 4.10 is available for download! If you are the kind of developer who likes to be on the bleeding edge, you will want to grab this latest build. With tons of new features and over 300 bug fixes, there is plenty in store.
To get started, head to the "Library" section of the Unreal Engine tab in the Epic Games Launcher, select "Add Versions", and choose 4.10 Preview 1.
For more information on the fixes included in the release, check out the update from Stephen Ellis on the Unreal Engine forums, and be sure to read up on the known issues list. As a reminder, the Preview builds are for testing only, and should not be used for the active development of your project.