Carbon molecular sieve (CMS) membranes offer key advantages over current polymer membranes for challenging gas separations. Excellent plasticization resistance and high selectivity with low permeance loss at subambient temperatures also make CMS attractive for potential hybrid post combustion CO2 capture technology. Here we describe highly permeable ultra-thin skin CMS (ULT-CMS) membranes with CO2 permeance > 3000 GPU at 35 degrees C and > 2500 GPU at -20 degrees C with 2-3x increase in CO2/N-2 selectivity at subambient temperaures. Dual layer polymer precursors fibers comprising Matrimid (R) with polyvinylpyrrolidone (PVP), a pore forming polymer, are used to create a substructure support, while 6FDA/BPDA-DAM polymer comprises the thin sheath layer. Two different skin thickness and outer diameter polymer precursor membranes were prepared by varying the spinning parameters to study the effect on CMS performance. Polymer precursor membranes were pretreated with 10% VTMS (vinyltriethoxysilane) to avoid substructure collapse and 0.1% DETDA (3,5-diethyltoluenediamine)/TMC (1,3,5 Bezenetricarbonyltrichloride) hybridization treatment is used to heal nanoscopic defects before pyrolysis. The precursor fibers, pyrolyzed at 550 degrees C, create highly permeable CMS membranes for CO2/N-2 separation with high selectivity at ambient and subambient temperaures as noted above.