This paper describes and evaluates a multistage adaptive testing (MSAT) design that was implemented for the Programme for International Student Assessment (PISA) 2018 main survey for the major domain of Reading. Through a simulation study, recovery of item-response theory model parameters and measurement precision were examined. The PISA 2018 MSAT design resulted in a parameter recovery as good as the operational benchmark, and measurement precision was improved by 4 to 5% with gains up to 10% at the extreme performance levels.