An article includes an asymmetric hollow fiber CMS membrane made by a method comprising: heating a polymeric precursor to a pyrolysis temperature from 500 °C to 1200 °C; pyrolyzing the polymeric precursor at the pyrolysis temperature, thereby forming a pyrolyzed polymeric membrane; exposing the pyrolyzed polymeric membrane to an atmosphere comprising ≥ 50 ppm oxidant; and cooling the pyrolyzed polymeric membrane to a cooling temperature that is ≤ 50 °C. The exposing and the cooling are performed sequentially or simultaneously, thereby forming the hollow fiber CMS membrane. The hollow fiber CMS membrane has a permeate/retentate selectivity ≥ 5 and a permeate permeability ≥ 50 GPU when measured while separating an analyte stream comprising the permeate and the retentate at a temperature from 20 °C to 30 °C.