Prepaid API gateway
How a prepaid API gateway prevents surprise AI bills
A prepaid API gateway checks available balance before routing a request. If balance or key budget is exhausted, the gateway rejects the request before it reaches an upstream model provider.
Prepaid vs invoice-based usage
Invoice-based systems may continue serving traffic and bill later. A prepaid gateway is stricter: no balance means no upstream request, which makes spend easier for small teams to control.
What balance protection should include
Balance protection should happen before routing and should work together with per-key budgets, model allowlists, max output caps, and request-level usage logs.
- Return 402 before upstream routing when balance is insufficient
- Do not bill balance or budget rejections
- Keep an auditable ledger for completed deductions
When prepaid works best
Prepaid gateways are useful for indie builders, SaaS trials, customer-facing agents, and internal tools where predictable spend matters more than unlimited usage.
FAQ
Does prepaid mean requests stop immediately at zero?
Yes. The gateway should reject new requests when available balance or configured key budgets are exhausted.
Does prepaid remove the need for logs?
No. Balance limits stop overspend, while logs explain which requests consumed credits.