Migration planning
OpenRouter Alternative Migration Plan for SaaS Billing Teams
A practical migration plan for SaaS teams moving AI API workloads from a shared model router to an OpenAI-compatible gateway with customer keys, prepaid balances, and usage billing.
When a migration is worth planning
OpenRouter-style aggregators are useful when a team wants quick access to many models through one API. The migration question usually appears later: finance needs customer-level invoices, support needs per-tenant usage explanations, product needs quota tiers, and engineering wants routing behavior that is tied to business policy instead of a single shared application key.
The goal is not to replace a working router overnight. A safer path is to introduce an OpenAI-compatible gateway layer that can mirror traffic, attach tenant metadata, enforce budgets, and gradually move production workloads behind customer API keys.
Migration inventory
| Area | What to capture | Why it matters |
|---|---|---|
| Models | Requested model IDs, fallbacks, prompt sizes, context length needs, and latency sensitivity. | Prevents a migration from silently changing quality, speed, or cost behavior. |
| Tenants | Workspace id, plan tier, billing owner, prepaid balance, monthly allowance, and overage policy. | Turns provider usage into customer-readable usage records. |
| Features | Chat, agents, enrichment jobs, summaries, coding tasks, and background workflows. | Lets teams assign different budgets and model tiers by product surface. |
| Keys | Current shared keys, service keys, test keys, and any customer-supplied BYOK credentials. | Reduces blast radius and makes rotation/audit practical. |
| Billing | Token accounting, cached tokens, provider invoice periods, currency conversion, and refund rules. | Prevents reconciliation surprises after switching traffic. |
A phased migration plan
- Mirror first: keep the existing API path but log tenant, feature, model, and estimated cost in the gateway.
- Issue customer API keys: map each tenant or workspace to a key so every request has an owner before it reaches a provider.
- Move one workload: start with a low-risk feature such as summaries or internal support drafts, not the highest-value production agent.
- Add budget policies: enforce soft limits, hard stops, model downgrades, and prepaid balance checks before provider routing.
- Reconcile invoices: compare gateway usage records against provider invoices for at least one billing cycle before expanding.
- Expand by segment: migrate tenants, features, or plan tiers in batches so rollback stays simple.
Compatibility checklist
- Keep the OpenAI-compatible request shape stable so SDK and agent changes are minimal.
- Document any model-name aliases instead of hiding them in application code.
- Return explicit errors such as
tenant_budget_exceededormodel_not_allowed_by_policy. - Preserve streaming behavior for chat and agent workloads that depend on partial output.
- Store provider response ids, selected route, fallback reason, token counts, and policy version for audits.
How this connects to billing controls
A migration is much easier when usage attribution is designed before the cutover. The gateway should know which tenant, feature, customer API key, model, provider, and billing period each request belongs to. For schema ideas, see the AI API usage attribution guide. For enforcement policy examples, see tenant-level AI budget guardrails.
Need an OpenAI-compatible migration path?
FerryAPI helps SaaS teams route model requests, manage customer API keys, enforce quotas, and track usage billing across providers without rewriting every client integration.