What are multi-armed bandits, and when do you use them instead of A/B testing?

Bandits optimize while they learn, shifting traffic toward winners mid-experiment instead of fixing it like an A/B test. The signal is the explore-exploit tradeoff, the three core algorithms, and knowing exactly when a bandit beats a clean A/B test.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.