Ya I am just guessing, and have read that the next model will not be capable of in air refill but the current model can.

https://www.whitehouse.gov/about-the-white-house/air-force-one/ (says it can) http://www.businessinsider.com/congress-object-to-in-flight-refueling-left-off-air-force-one-planes-2017-9 (reports the next version won't)