From
https://www.ctbuh.org/resource/height : "…the architectural top of the building, including spires, but not including antennae, signage, flagpoles or other functional-technical equipment. This measurement is the most widely utilized and is employed to define the CTBUH rankings of the World’s Tallest Buildings."
Regarding Wikipedia, I wouldn't assume that it's an unreliable source of information, because its accuracy is improved by the fact that it's constantly undergoing peer review. For this reason, Bill Nye the Science Guy has even said that he trusts Wikipedia more than traditional encyclopedias. I disagree with him for the less visited Wikipedia articles, but he's probably right for the frequently visited ones.
That article about One Chicago may not be very up-to-date, although it does have the latest height of 971 ft.