The runtime of the exhaustive search was ∼2332 hr. By comparison, MFBO incurred 2.5% of the runtime of the exhaustive search. Two-stage screening. A two-stage search (1) runs a low-fidelity simulation of Xe/Kr adsorption in each of the 609 COFs in X , then (2) (a) sorts the COFs according to their low-fidelity simulated Xe/Kr selectivity, in descending order, then (b) queues this list of COFs for high-fidelity simulations of Xe/Kr adsorption, working down the list. This search strategy leverages the cheap, low-fidelity simulations available in stage (1) to recover the optimal COF early in the sequence of stage (2). However, this strategy still fails to leverage the information contained in the simulation data D [n] as the search proceeds to (i) avoid running low-fidelity simulations in every COF during stage ( ) and (ii) adjust the sequence of highfidelity simulations as high-fidelity simulation data is collected in stage ( ).