The riser with its 1-1/8" diameter sits on top of the threaded nut. So the steerer bit that sticks up is 1" in diameter. I can't say right now if it steps or not, I thought not, but I will check for you.
It has to because it's the only possible way for a 1" ID riser to fit a 1-1/8" fork/headset. The
Xootr website also lists the following spec "CroMoly straight
taper fork".
I guess that explains why everyone who has done a fork swap is using a Airnimal Joey riser or similar because the Xootr riser won't fit on an untapered 1-1/8" fork.