I need advice about constructing concrete stairway in hill side. 5" rise, and 12" run. 9 treads 48" wide and 4" thick w/ 4" wide beams at each side. Do I need to use rebar, or wire mesh? No frost.

I have not to decided to excavate steps into the hillside, and pour over them (sand between concrete and the soil), or excavate a slope under the stairs. I think a flat slope would better isolate the stairs from the underlying soil that has a high shrink swell factor. What keeps the concrete at the top stair from flowing down to the bottom of the stair during the pour