I wasted a lot of time yesterday and today until Mark Knopper pointed me to a solution for updating my beta by hand. Like others, my download had stalled at 151MB (of a 1+GB update) and I needed to just get the update done.
That solution thread linked to another developer forums post here. This thread contains links to manual downloads. Once you download the component pieces directly, you can move them into the stalled download in /Library/Updates, and then reboot and click Update in App Store.
I decided to complete all downloads, although some report you only have to install three of the four links. App Store sees the completed downloads, and installs and updates. I am now running Beta 2.
Some in that discussion thread have reported unstable systems after performing a manual upgrade. “I may have jinxed myself by asking, but after attempting to apply the packages willy nilly, it seems that my environment (16A201w on pro 3,1) is very unstable. Safari is now crashing all the time.”
My A/C is broken and the repair person is about to arrive so I won’t have time to test my upgrade until later today or maybe early next week. If you do go this route, do so with extreme caution.