Preview 5 of 4.12 has been released! This build contains new features including a Foliage scalability setting, a Twist Corrective animation node that can drive curve values, such as Morph Targets, based on the twist of one bone relative to another, and the Pixel Inspector tool which lets you click on a pixel in the scene and visualize the material and rendering state that contributed to its colour.
If you have a Preview version already installed, simply hit 'Update'. If not, go to the Epic Games Launcher and select the "Library" tab. Click "Add Versions" and choose 4.12 Preview 5.
Check out the updates included in this release through the latest forum post from Stephen Ellis. Also be sure to have a look at the known issues list. Please remember, Preview builds are for testing only and shouldn't be used for the active development of your project.