Gradual Rollout

A gradual rollout is a method in which a change reaches a small share of users first and, if it stays healthy, is expanded step by step rather than shipping to everyone at once.

A gradual rollout is not about learning an effect but about limiting damage: if a change brings an error or a metric drop, only 1% of users are hurt, not all. This is why it is confused with an A/B test, but its goal differs; a test wants to know which is better, a gradual rollout wants to be sure the version about to become universal does not break something. Its key is having guardrail metrics: error rate, page speed and one business metric watched at each step, so if they worsen the rollout is paused or rolled back. A gradual rollout without these guardrails is merely a delay, not a safeguard.