Percentage rollout

Also called: percentage-based rollout, gradual rollout

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A percentage rollout exposes a feature to a configured share of users — say 10% — instead of everyone at once. Membership is decided by a deterministic hash of the user identifier and the flag key, so the assignment is stable: the same user always lands in the same bucket for the same flag.

How the bucketing works

The SDK hashes the user identifier together with the flag key into a stable bucket from 0–99. A 10% rollout serves the new variation to buckets 0–9. Because the hash is deterministic, raising the percentage to 25% adds users to the enabled cohort without re-randomising the original 10% — a property called sticky bucketing. This is what makes a rollout safe to ramp and safe to compose with experiments. The mechanics are covered in the rollout strategies guide.

Percentage rollout vs progressive rollout

A percentage rollout is the mechanism — a flag set to serve N% of traffic. A progressive rollout is the practice of stepping that percentage up over time (1% → 5% → 25% → 100%) while watching metrics at each tier. You need a percentage rollout to run a progressive one; the percentage is the dial, the progression is how you turn it.

Want the full picture? Read the concept guide: Rollout strategies →

Related terms

Feature flag

A feature flag is a conditional in your code whose value is controlled from a remote dashboard, letting you turn functionality on or off without deploying new code.

Dark launch

A dark launch ships a feature to production turned off or invisible to users, so the code runs in the live environment before anyone sees it — you reveal it later on your own schedule.

Kill switch

A kill switch is a feature flag used to disable functionality instantly in production — flip it off and every SDK stops running the risky code path within seconds, no redeploy required.

Browse the full feature flag glossary →

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