A/B Testing vs Bandits

A/B testing versus bandits is an experimentation trade-off: fixed-allocation tests are better for clean inference and long-term decisions, while bandit tests are better for short-term reward maximisation when opportunity cost is high.

Key points

• AB Tasty describes classic A/B testing as exploration-heavy: traffic is split across variations until there is enough evidence to declare a winner ^[src-022].
• Multi-armed bandits exploit earlier by shifting traffic toward better-performing variations during the test, which can reduce conversion loss from underperforming variants ^[src-022].
• Bandits are preferable when time is limited, content is short-lived, there are many variations, or each lost conversion carries high opportunity cost ^[src-022].
• Traditional A/B testing remains more useful when the goal is statistical significance, post-experiment analysis, critical business decisions, or long-term campaign learning ^[src-022].
• There is no universal winner. The choice depends on objective, resources, time pressure, technical expertise, and whether the main priority is learning or maximising reward during the experiment ^[src-022].
• Braze gives the complementary operating model: A/B testing is better for foundational validation and broad campaign direction, while bandits are better for adaptation and live refinement once a direction exists ^[src-027].
• In that model, A/B testing might choose a homepage layout or campaign concept, while bandits refine elements such as images, headlines, buttons, offers, channels, or segments as performance data arrives ^[src-027].
• Statsig adds a third option inside classic experimentation: keep fixed-allocation A/B tests, but run them in parallel when product-experience risks are controlled and Treatment Interaction Effects are checked statistically ^[src-029].
• This narrows the contrast with bandits: sequential A/B testing is slow, but Parallel A/B Testing can increase throughput while preserving the inference-oriented strengths of A/B tests ^[src-029].
• Statsig’s acceleration article further narrows the gap by combining classic tests with faster methods: concurrency, proxy metrics, variance reduction, sequential testing, and contextual bandits for shallow winner-selection decisions ^[src-031].
• In that framing, bandits are not a replacement for every A/B test; they are useful when the decision rule is simply to push traffic toward a quantitative winner rather than perform a careful calibration study ^[src-031].

Related entities

• Braze
• Statsig

Related concepts

• Multi-Armed Bandits
• Dynamic Traffic Allocation
• Exploration-Exploitation Trade-off
• Offline Policy Evaluation
• Marketing Bandit Optimisation
• Intelligent Selection
• Parallel A/B Testing
• Treatment Interaction Effects
• Experiment Statistical Power
• A/B Test Acceleration
• Proxy Metrics in Experiments
• Experiment Variance Reduction
• Sequential Testing

Source references

• ^[src-022] AB Tasty — “Multi-Armed Bandits: A/B Testing with Fewer Regrets”
• ^[src-027] Team Braze — “What is a multi-armed bandit? Smarter experimentation for real-time marketing”
• ^[src-029] Allon Korem and Oryah Lancry-Dayan — “You can have it all: Parallel testing with A/B tests”
• ^[src-031] Yuzheng Sun — “Speeding up A/B tests with discipline”