LLM API Gateway

The gateway receives a model request, authenticates the caller, applies policy and forwards it to an eligible endpoint. It may normalize request formats and return usage information for accounting. Routing can distribute traffic among deployments or choose alternatives after failures. This differs from an inference engine, which executes the model, and from an SDK, which runs inside the application. A common interface does not make every provider semantically equivalent: tool calling, streaming, structured output and safety behavior may differ. The gateway must expose or constrain those differences deliberately rather than silently promising portability.

The practitioner defines application identities, allowed models, rate limits and routing rules. Fallbacks need tests against required capabilities and data-location policies. Useful outputs include gateway configuration, request traces and per-application usage records. Failure handling should distinguish authentication errors, provider throttling and retryable service failures. The system must avoid logging sensitive request content unnecessarily and should measure the added latency. Capacity tests cover concurrent clients and a failed upstream to verify that centralization does not create an unexamined bottleneck.

A gateway can become a single point of failure or hide the real cause of provider errors. Aggressive retries can amplify throttling and cost. Interface compatibility does not prove output equivalence, and cached pricing data may misstate expenditure. Quality includes tested routing, correct authorization and transparent operational status. Central policy helps manage access, but application-level correctness and the suitability of a fallback model still need evaluation on the actual tasks.