A blurb in a recent APC press release at IAH notes this at the bottom:
http://www.fly2houston.com/0/3921678/0/83280/
The Houston Airport System and U.S. Customs and Border Protection have recently launched several different partnerships designed to expedite the arrivals process for international passengers. The City of Houston stands as one of the most active areas in the country in regards to participation in the Global Entry program. IAH is one of only two airports in the nation to offer expedited entry through a program called OneStop and Houston was the first city chosen to be a “Model Port of Entry.”
It does not get into specifics of what Chicago has but notes IAH and "another airport" (ord) are the only ones with One-stop.
I know IAH One-stop allows int'l-int'l connections on UA to skip the checked bag step and use the "back end" exit where you skip the customs exit line and can then enter the int'l only TSA line.