The gravel bed is in place, the moisture barrier has been laid on top and the reinforcing mesh placed on top of that. I was expecting the reinforcing to be made up of 1/4"/6mm bar and be delivered in 4'x8'/1.2mx2.4m sheets but it was much thinner, more like coat-hanger wire and delivered as a roll. I couldn't find any US building standard that specified the characteristics of reinforcing for basement slabs though I did find that Saskatchewan, Canada doesn't require any at all. The concrete is supported over its entire surface so the reinforcing is apparently not for strength but to limit cracking.
I was also slightly concerned that the reinforcing mesh was not raised so that it would be in the middle of the set concrete. I've seen supports that look like 4-legged spiders for the heavy grid style reinforcing but they are used on top of plywood formwork for above-ground construction; if used here they would puncture the moisture barrier as soon as someone stepped on them which would happen when the workmen were getting the concrete hose to the back.