How to Evaluate One Gateway API for OpenAI Claude Gemini Fallback Routing

To evaluate a gateway API for routing between OpenAI Claude, Gemini, and other models, follow these steps:

1. Define a unified gateway with a single credential and chat contract. This simplifies the system by requiring only one API key to manage and one consistent conversation format across models.

2. Choose a primary model and a fallback model from the available catalog. The primary model should be the one best suited for the specific task, while the fallback model provides redundancy and reliability.

3. Keep the application focused on treating the output as structured data, not just a helpful paragraph. Ensure that the gateway extracts specific fields such as supplier_name, invoice_number, invoice_date, currency, subtotal, tax, and total.

4. Implement a mechanism for controlled fallback. Only route to the fallback model if both the primary and fallback models return the same structured fields. This ensures that the output contract is preserved and that the fallback is useful only when necessary.

5. Check EU and US processing requirements separately to ensure compliance and avoid any legal issues.

6. Consider the incident pattern where a rate-limit response causes the system to retry another model. The dashboard should report which model answered, what schema it satisfied, and whether the retry preserved the invoice contract.

7. The gateway should solve a bounded job: extracting specific fields from supplier invoices for a customer-support workflow. This ensures that the system is focused and efficient.

8. When designing the gateway, consider the following shapes:

- OpenAI direct API: Direct access to a single model family, best when the application owns other credentials, adapters, and fallback logic.

- Anthropic Claude direct API: Direct request semantics for Claude, suitable for cross-vendor routing if Claude is the deliberate boundary.

- Google Gemini direct API: Direct Gemini request semantics, ideal when Google is the platform boundary and a unified gateway is needed.

9. A unified gateway offers several advantages, such as reduced credential lifecycles, a single REST API, and a self-describing discovery surface. This makes it easier to inspect the catalog and schemas before treating a model as a valid fallback.

10. However, the gateway is not always the best solution. If a vendor's native controls are non-negotiable or if there are specific requirements like audio transcription or realtime voice sessions, a direct integration might be more appropriate.

11. Ensure that the gateway handles quality and rate limits properly. Classify failures before changing models, with a 429 status code indicating a need for backoff and respect for the Retry-After header. For schema failures, validate the response and decide whether to retry with a different model. Ordinary client errors should surface the response body rather than disappearing into a generic retry.

12. Use Go to implement the gateway. The provided code snippet demonstrates how to discover the model list, retry rate limits with exponential backoff, check non-success responses, and send the same extraction prompt to a primary and then a fallback model. The model IDs are fetched from the environment, making the catalog availability a live state.