At first initialization, for me it was indicating approximately 4gb.
I thought for a moment that this wasn’t so bad after all. I left my desk for a few moments but when I returned I got a shock in an inexplicably mysterious change that jumped to 40gb.
At that point I paused the download.
I came back a day later and began running the update again, but decided to check the download graph in my Steam account.
To my surprise it indicated approximately 12+ gb, So I let it run till it completed.
After that, I went to my ATT account to check how much of my data allowance was used up with this download and found it to be roughly 16gb. (Double that of my previous inquiry of data usage at roughly 8gb before beginning the download).
In allowing for any web browsing after yesterday’s pause, I can safely guestimate the download was closer to 12+gb as shown on my Steam download.
It’s still a lot, but at least this was more tolerable than what happened the month prior.

In comparison, it seems we’re roughly in the same “ball-park”.