Warning: Beta features are subject to change.
Activating beta features for GitHub Apps
-  In the upper-right corner of any page, click your profile photo, then click Settings.  
-  In the left sidebar, click Developer settings.  
-  Select the GitHub App you want to enable a beta feature for. 
-  In the left sidebar, click Beta Features.   
-  Next to the beta feature you want to enable for your app, click Opt-in.  
Activating beta features for OAuth Apps
-  In the upper-right corner of any page, click your profile photo, then click Settings.  
-  In the left sidebar, click Developer settings.  
-  In the left sidebar, click OAuth Apps.  
-  In the left sidebar, click Beta Features.   
-  Next to the beta feature you want to enable for your app, click Opt-in. 