<p>Unsteady bulging in continuous casting of steel slabs refers to transient bending of the strand shell between the rolls of the secondary cooling zone. It can cause defects in the final product, impacting surface quality and structural integrity, and is thus unwanted. Because roll pitches significantly influence unsteady bulging, optimizing these pitches might avoid or at least reduce this phenomenon already in the design process. In this respect, the literature in this field lacks a systematic method for selecting the roll pitches. The current work proposes a two-step multi-fidelity method for selecting individual roll pitches for each roll pair of a continuous slab caster, based on an optimization problem and an unsteady bulging model . Simulation results using a model validated at a real plant show that the optimized roll pitches can avoid unsteady bulging for a wide range of system parameters and are, in this respect, superior to uniform roll pitches. The proposed method can be readily transferred to other continuous slab casters, particularly supporting the design of new installations. Dedicated experimental validation of the optimized roll pitch layouts in existing plants would require major plant modifications and is therefore outside the scope of this work.</p>