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A successful handover is a boundary, not a finish line. Once the successor queue surrogate becomes operational, its traffic mix, routing inputs and decision thresholds can move away from the qualification trial. The retired champion still contains useful evidence, but it must not quietly regain authority. A monitored post-handover system therefore needs three linked controls: drift signals for the live successor, a fresh challenger that is not trained on the same failure, and an archive rule that preserves the old champion without letting it make unrecorded decisions.
Open the chapter contents · Queueing Theory root · Gold Standard of Education · How X Works
Chapter contents
Choose the route closest to the decision, or read from Chapter 1. The chapters remain open; these grouped routes are a navigable index.
Route 1 · Define the decision
Route 2 · Work the ledgers
Route 3 · Transfer the method
Route 4 · Check limits and evidence
Route 5 · Ask and continue
CHAPTER 1 OF 12 · DEFINE THE DECISION
1. Define the post-handover monitoring claim
State what must remain true after handover: the successor is being used inside its approved queue domain, its decision loss stays within tolerance and the implementation matches the frozen qualified version. A model can remain numerically accurate while the operational decision boundary changes around it.
Separate input drift, relationship drift, implementation drift and outcome drift. One alert cannot diagnose all four. Each signal needs an owner, a review window and a declared action.
CHAPTER 2 OF 12 · DEFINE THE DECISION
2. Give the archived champion a controlled role
The retired champion may serve as a frozen shadow comparator, replay baseline or source of historical stress cases. It must not route live work or override the successor unless a documented fallback activates.
Archive code, dependencies, calibration data, supported domain, known failures and the exact date operational authority ended. If the champion is rebuilt with a new library or input transformation, it becomes a new artefact rather than the archived reference.
CHAPTER 3 OF 12 · WORK THE LEDGERS
3. Build a drift-and-authority ledger
A support queue monitors the first six weeks after successor activation.
| Signal | Week 2 | Week 4 | Week 6 | Authority response |
|---|---|---|---|---|
| Arrival-mix distance | 0.07 | 0.11 | 0.19 | Investigate peak segment |
| Action disagreement with archive | 4% | 6% | 14% | Shadow review only |
| Realised excess loss | 0.2 | 0.3 | 1.1 | Freeze expansion |
| Implementation hash | Matched | Matched | Matched | No code alarm |
The week-six pattern points to a changed traffic segment rather than an implementation mismatch. Expansion pauses while the team isolates the affected regime.
CHAPTER 4 OF 12 · WORK THE LEDGERS
4. Worked challenger-refresh decision
The team can refresh a challenger using three evidence blocks: old qualification data, recent drifted traffic and a reserved future week. It compares decision regret under the current successor and two refresh designs.
| Candidate | Development evidence | Reserved-week regret | Peak constraint breaches | Decision |
|---|---|---|---|---|
| Live successor | Original trial | 1.8 | 3 | Keep as champion during review |
| Refresh A | Original + weeks 1–5 | 0.9 | 1 | Advance to shadow trial |
| Refresh B | Weeks 4–5 only | 0.6 | 4 | Reject: unstable tail |
| Archived champion | Frozen history | 2.4 | 2 | Comparator only |
The reserved week is not reused for tuning after the first comparison. If Refresh A changes, it needs new confirmatory evidence.
CHAPTER 5 OF 12 · WORK THE LEDGERS
5. Refresh the challenger without chasing noise
A refresh should answer a named drift mechanism. Reweighting, recalibration, feature repair and structural replacement solve different problems, so the change log must connect each intervention to evidence.
Use traffic strata and decision-sensitive metrics. Repeatedly retraining on every alarm can turn monitoring noise into model churn and make the archive impossible to interpret.
CHAPTER 6 OF 12 · TRANSFER THE METHOD
6. Set escalation, rollback and fallback boundaries
Predeclare what freezes expansion, what narrows the supported domain and what triggers fallback. A rollback target can be a simple rule or capacity floor; it need not be the retired champion.
When the archived champion is the fallback, record the conditions under which its known weaknesses are less harmful than the successor’s current failure. Time-limit that exception and log every decision made under it.
CHAPTER 7 OF 12 · TRANSFER THE METHOD
7. Changed-context transfer: cloud autoscaling
Transfer the method to a cloud queue where a successor surrogate controls replica requests. A new product launch changes burst size and cold-start delay, while the code hash remains unchanged.
The transfer check separates the arrival shift from actuator delay, keeps the former champion in shadow and qualifies a refreshed challenger on burst and cold-start strata before changing control authority.
CHAPTER 8 OF 12 · TRANSFER THE METHOD
8. Connect qualification, retirement and monitoring
Begin with the successor qualification and handover guide. Use the surrogate retirement guide to preserve the reason the former champion lost scope.
Return to the screening and confirmatory experiment guide when a refresh changes the model structure rather than only its calibration.
CHAPTER 9 OF 12 · CHECK LIMITS AND EVIDENCE
9. Limits and common misconceptions
Drift is not proof of harm, and a harm signal is not proof of model drift. Operational changes, data delays and interventions can alter outcomes without changing the surrogate relationship.
The archived champion is not an oracle. Its disagreement can reveal change, but the same drift may make both models wrong.
CHAPTER 10 OF 12 · CHECK LIMITS AND EVIDENCE
10. Practical evidence checklist
Preserve the successor version, qualification scope, live input schema, monitoring baselines, traffic strata, metrics, thresholds, alert history and realised decision outcomes.
For every refresh, save the drift diagnosis, development data, untouched confirmation, constraint checks, authority decision, fallback, archive access log and next review date.
CHAPTER 11 OF 12 · ASK AND CONTINUE
11. Frequently asked questions
Should the retired champion keep running?
Only when the diagnostic value justifies the cost and the shadow role is technically separated from operational control.
When does a refresh become a new successor?
When its structure, intended use or evidence basis changes enough that the old qualification no longer supports it. Treat the boundary explicitly.
Can drift thresholds change?
Yes, through a governed revision using evidence that is separated from the window used to judge the change.
CHAPTER 12 OF 12 · ASK AND CONTINUE
12. Sources and next reading
The Federal Reserve’s 17 April 2026 revised model-risk guidance addresses model inventory, independent validation, outcomes analysis and ongoing monitoring in its regulated context. NIST’s AI RMF Playbook covers measurement against deployment conditions and post-deployment risk management. The ledgers here are original teaching examples.
Continue through the Queueing Theory root, the Gold Standard of Education and How X Works.
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