How much space needed for Mac OS 10.16?

I just upgraded to 10.15.6 beta 3 then straight away I'm offered 10.16! There is no 10.16 on the dev website. When I try installing it says it needs another 7Gb. There is already 53Gb available, so what is going on here? I've also read that 10.16 is actually Bug Sur beta masquerading as Catalina and I haven't elected to beta test Big Sur so, again, what is going on?
I have raised a bug report for this: FB7849024
How much space needed for Mac OS 10.16?
 
 
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