What Is an AI API Gateway (Relay)? How base_url Switching Works

Q: Do I have to change my code to switch models?

No. You change the model parameter to the model you want. Everything else stays the same.

An AI API gateway (also called an API relay, aggregator, or proxy) is a middle layer that puts many AI model providers behind a single, OpenAI-compatible endpoint. Instead of juggling separate keys, SDKs, and billing for OpenAI, Anthropic, Google, DeepSeek, and xAI, you use one API key and one base URL to reach all of them.

This guide explains what a gateway does, why teams adopt one, and how migrating usually takes only a single line of configuration.

What an AI API gateway actually does

A gateway sits between your application and the upstream model providers. When your app sends a request, the gateway:

Normalizes the protocol so every model is callable in the OpenAI Chat Completions (and increasingly the Responses) format.
Routes the request to the correct upstream provider based on the model parameter.
Meters usage per key, model, and provider for billing and analytics.
Handles failover by retrying on an alternate upstream when one provider returns errors or times out.
Centralizes keys and logs so you can audit traffic and rotate credentials in one place.

In short, the request path is simple: your app → gateway → the right upstream provider (OpenAI, Claude, Gemini, DeepSeek, and more) → back to your app, all through one consistent interface.

Why developers use a gateway

One key, hundreds of models

You register once and can call GPT-5, Claude, Gemini, DeepSeek, Qwen, Llama, and more by changing the model string. No separate onboarding for each vendor.

Lower cost

Good gateways buy capacity in bulk and pass the discount on. For many models, relay pricing undercuts official rates by 30-80%, which is significant at scale.

Reliability

If an upstream provider has an outage, the gateway can automatically route to a healthy backup, so your product keeps working.

Access from restricted regions

For developers in regions where some providers are hard to reach directly, a gateway with multi-region nodes provides stable connectivity without per-vendor workarounds.

How base_url switching works

Because a quality gateway is OpenAI-compatible, you usually do not rewrite any code. You only change two things:

The base URL to the gateway endpoint (for example https://api.your-gateway.com/v1).
The API key to the one issued by the gateway.

Here is a typical Python example:

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_GATEWAY_KEY",
    base_url="https://api.your-gateway.com/v1",
)

resp = client.chat.completions.create(
    model="gpt-5.4-mini",
    messages=[{"role": "user", "content": "Hello!"}],
)
print(resp.choices[0].message.content)

The same idea applies to Node.js, Go, and any framework that speaks the OpenAI protocol. Switching the model from gpt-5.4-mini to claude-sonnet-4-6 or deepseek-v4 is just a string change.

When a gateway is the right choice

A gateway is a strong fit when you:

Use multiple model families and want one billing and logging surface.
Care about cost and want bulk-discounted rates.
Need failover for production reliability.
Want to experiment across models without re-integrating each vendor SDK.

If you only ever call a single model and need every native, bleeding-edge parameter the moment it ships, going direct to that one provider can still make sense.

What to check before you commit

Pricing clarity: Are per-model rates and billing rules documented?
Model coverage: Does it support the exact models and tools (Claude Code, Cursor, Codex) you use?
Stability: Is there an SLA, multi-node routing, and failover?
Payments and invoices: Does it support your payment method and issue invoices?
Observability: Can you see per-key usage, latency, and export logs for audits?

FAQ

Is an AI API gateway compatible with the OpenAI SDK? Yes. A well-built gateway implements the OpenAI request format, so you keep your existing SDK and only change the base URL and key.

Do I have to change my code to switch models? No. You change the model parameter to the model you want. Everything else stays the same.

Is a gateway slower than calling providers directly? A good gateway adds minimal overhead and can be faster in restricted regions thanks to nearby nodes and smart routing.

Ready to try it? TokenVoke gives you one OpenAI-compatible endpoint for 40+ providers. Browse the Model Square for live pricing or read the docs to send your first request.