Steam Community: Experimental Branch 16/06 by Hello Games
https://steamcommunity.com/app/275850/discussions/0/567037313987936597/

Experimental Branch 16/06 :: No Man's Sky General Discussion
Hello Everyone, First of all, thanks so much to everyone who has already spent time playing No Man's Sky and letting us know about any issues you've experienced. To play in Experimental, right-click on No Man's Sky from the Steam library page and select "Properties". Among the available tabs will be the "BETAS" tab. Enter "3xperimental" in the textbox and press "CHECK CODE", then select it from the dropdown menu.