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The multi-armed I-SPY 2 breast cancer clinical trials are starting to fulfill the promises of smarter, more efficient, biomarker-driven trials long touted by reformers (Nat. Biotechnol.25, 287–292, 2007). I-SPY 2 has now sped six drug candidates or combinations to phase 3 and has inspired a generation of Bayesian adaptive platform trials beyond breast cancer applications.