After the gravel, the next step was to lay down a vapor barrier and cover the entire footprint of the foundation in a 2" thick layer of foam panels.
Next step - take rebar...
...and tie it up in a grid.
Those red tubes you see there is PEX for the hydronic heating system. It's tied to the rebar.
All the pipes feed into the mechanical room of the house:
After this work gets approved by the city, it can be buried in 8" of concrete. This will hopefully happen later in the week!