As of today, there are 12 states which operate their own full ACA exchanges, including their own board of directors, marketing budget, bylaws and tech platform for their enrollment website. 34 states have offloaded just about all of that to the federal exchange, HealthCare.Gov. And then there are five states which are in between: They have their own state-based exchange...but their tech platform is basically piggybacked onto the federal exchange: Arkansas, Kentucky, Nevada, New Mexico and Oregon.
Arkansas and New Mexico always planned on moving off of HC.gov onto their own full exchange platform but never got around to doing so. Kentucky's ("kynect") was working perfectly well from day one, and only made the move to the federal platform after three years because new GOP Governor Matt Bevin decided he didn't like it for whatever reason. New Mexico and Oregon, meanwhile, had such major technical problems at launch that they scrapped their sites after the first year and moved to the Mothership. (As an aside, Hawaii also scrapped their exchange site after the second or third year, but they shut down their entire state-based exchange and moved everything to HC.gov).