Separate decision simulation from response changes
The production call follows its current model choice. In parallel or asynchronously, the gateway classifies the request, chooses a hypothetical route, and records the expected price. For sampled requests, it can also run the alternative model and compare outputs.
Not every request needs a second paid call. Begin with decision simulation, then concentrate paired evaluations on high-volume and uncertain cohorts.
Build a shadow ledger
Record the baseline model and cost, hypothetical model and cost, applicable policy, classifier confidence, and whether the request was eligible. Keep estimates separate from realized savings. A dashboard should never present shadow savings as money already saved.
The ledger also reveals missing context: unclassified routes, unsupported modalities, long-context outliers, and teams with no stable ownership.
Define promotion gates
A route moves from monitor to assist or enforce only after it has enough representative samples, acceptable quality delta, schema and tool success, latency within target, and an approved rollback. Promotion should occur per team and route family, not as one organization-wide switch.
- Representative traffic window
- Golden-set and production-sample results
- No material cohort-specific quality cliff
- Known effective cost after retries
- Named owner and rollback threshold
Keep shadow mode available
After launch, new models, price changes, prompt revisions, and policy updates should return to shadow comparison. Monitor mode is not merely an onboarding stage; it is the safe state for revalidation.
Frequently asked questions
Does shadow mode save money immediately?
No. It measures potential savings while production behavior remains unchanged. Realized savings begin only when a route is approved for enforcement or caching.
Does shadow mode double model cost?
Only if every request runs through both routes. A cost-conscious design simulates decisions broadly and runs paired model calls on a controlled sample.
How long should shadow mode run?
Long enough to capture representative cycles and edge cases. Use sample sufficiency and cohort coverage rather than a fixed number of days.
Sources and further reading
FrugalAI uses primary documentation and published research where possible. Product capabilities and prices can change; verify vendor details before procurement or production changes.