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System Design

Deployment & Rollout

How a running LLM system ships a model or prompt change with evidence: version manifests, mirroring and replay, canary sample arithmetic, failure-mode-first triggers, one-move rollback and the GPT-4o case.

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Production11 min readFirst readScaling 10k to 1MThe Eval Stack

After this section you can

  • Choose a mirror, a canary or a pointer flip for a change, and defend it on evidence and blast radius
  • Derive how long a canary must hold from its traffic share, judged fraction and the drop you need to see
  • Write failure-mode-first triggers and trace the GPT-4o rollback through them
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Deployment & Rollout

Ship a model or prompt change on evidence: mirror it, let judged samples set the hold time, and undo it with one move.

Key idea

A release is a manifest with immutable versions and one movable label. Every request logs its version. Move traffic in stages that wait for judged samples (responses a judge model has scored), not the clock, and roll back by setting the label, never by toggling it.

Each rung must earn the next with evidence; a failed rung sends the label back
FIVE RUNGS, ONE LABEL Offline gate eval suite passes Replay real requests no users see it Canary 1 to 5% of users judged samples Ramp 25 to 100% gate at each step Soak full traffic triggers still on Label: last-good set it, never toggle any failed gate

Amber gate, blue replay, teal canary and ramp, green soak, purple label, red abort path. Pans sideways on a phone.

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