Don't you see it listed below 3.0 as in this image:
The beta IS available for download. You just have to scroll to the bottom of the released versions listed on https://developers.arcgis.com/en/downloads/ to get to the beta.
I went to that page. I still don't see the beta available for download, just 3.14.
I feel brilliant now. I did not click on the dropdown. Thanks.
Perfect, Thanks !
Retrieving data ...