The collapsing dial pad was there in older versions as well. The new UI is the that the unlock circle is now used to answer or reject incoming calls. I didn't wipe, but I did go into settings > apps and clear data for call settings and everything that starts with "phone" immediately after updating and I got the new UI. Not sure if doing this is even necessary, but at least you don't have to do a full wipe to get it.
A screenshot was posted in the news section a few weeks back, although the current implementation looks slightly different.