My commute was pancake-flat 8 miles, trail-to-highway shoulder-to-trail. I pushed; not super hard, but enough I was definitely working, 3 to 5 days per week, sometimes round trip. My speed increased over time, but the real tell was when I rode a 5-mile loop with some "challenging" hills (i.e. ride a bit, pause to breathe, ride a bit, etc.) and not only did I not have to stop, but I had a gear leftover! On a different road is a short very extremely steep hill, and again no stopping, with a gear in reserve. I was quite shocked.

So yes, your commute can be a workout. Have fun!