They are gloss black. Previously mine was the "vinyl black pack" but I had it all removed and painted gloss black. I did have protection film put on that covers it on the lower rocker panels to keep the chips away but you won't ave to worry about that. My old vinyl held up really well in the area.
Yea my 2018 is matte black. I just ordered carbon fiber side sills, was torn on which way to go since I went with gloss black splitter. Would have preferred carbon there also but couldn't get with winglets but the gloss black does go well with the gloss black on bumper at least. I'm also doing carbon fiber side scoops so I think my new CF sideboards should go good with those and my CF rear hatch and front access panel. Oh and also just ordered a carbon fiber diffuser finisher. And to think when I bought this car 2 months ago wasnt planning on modding, that plan never seems to work