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When you send a request to https://gateway.ngrok.ai, the model field tells the AI Gateway which model to call. Use a model ID when you want the gateway to resolve the provider from the model catalog. Use provider:model when you want to choose the provider yourself.

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Use a model ID

Use a model ID when you know which model you want to call and don’t need to force a specific provider. 
{
  "model": "gpt-4o",
  "messages": [{"role": "user", "content": "Hello"}]
}
The gateway looks up gpt-4o in the model catalog, selects the matching provider, and routes the request upstream.

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Route to a specific provider

Use provider:model when you want predictable routing or need to avoid ambiguity between model names. 
{
  "model": "openai:gpt-4o",
  "messages": [{"role": "user", "content": "Hello"}]
}
In this example:
  • openai is the provider ID.
  • gpt-4o is the model ID.
Use this format when you have more than one provider configured, want to call a custom provider, or want the request to go to one specific upstream.

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Use a custom provider model

{
  "model": "my-ollama:llama3.2",
  "messages": [{"role": "user", "content": "Hello"}]
}
Custom providers use the same provider:model format. In this example, my-ollama is your custom provider ID and llama3.2 is the model ID configured on that provider.

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Check model capabilities

Before choosing a model, check the model catalog for:
FieldUse it to check
Context windowHow much input the model can accept
Output tokensHow much output the model can return
ModalitiesWhether the model supports text, image, audio, video, or files
Provider key requiredWhether you need to bring your own provider key

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Keep access rules in mind

The request can only use providers and models allowed by the access key configuration assigned to the access key. If you need to limit what a client can call, see Restrict providers and models.

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Next steps