Here's how to opt in and play the latest experimental branch.
Open your steam client.
1.Click on Games/View Games Library
2.Right click ‘7 Days to Die’ and select properties
3.From the new popup dialogue box select the ‘BETAS’ Tab
4.Under ‘Select the beta you would like to opt into’ latest_experimental
The game will then update and download the latest experimental build Alpha 16 Experimental
Switching back to the latest main stable build is as easy as repeating steps 1-4 and on step 4 choose the option ‘None – Opt out of all Beta Programs’ and you’ll revert to the latest stable build.
Official Alpha 16 Release notes!