On the rules page of SCCA.com you can find the DRAFT version of 2018 rules, not the final version yet. https://www.scca.com/pages/solo-cars-and-rules

The highlight for Abarth drivers is the new STH or Street Tire Hot Hatch class, which includes the Abarth, both the Fiesta and Focus STs, and a bunch of other similar-ish cars.

I haven't read all the rules but heard something about looser restrictions on ECU tuning in the Street Touring categories, so as always, read the rules and ask questions.