The base is usually crushed compacted stone topped with compacted gravel. They then add 3-4 inches of sand and compact that. The sod itself has been grown in pretty rich top soil. Once the roots reach down into the sand and establish themselves the surface becomes pretty stable. Might be some chunks torn out during the season but I think this has more time than the last field. It will drain really really well.

https://twitter.com/BryanGHopkins/status/1783477714554593629