Using routing policies

A routing policy isn’t sent in the request body. Gateway resolves it for you on every call based on what you attach to the request and what’s configured on your org. This page covers how that resolution works and what you can do from the request side.

How routing policies are applied

Routing policies are attached to projects or set as the org default. When Gateway receives a request, it resolves the policy in this order:

1. Project-scoped policy. If the request includes a project (via the project_id body field) and that project has a routing policy, Gateway uses it.
2. Org default policy. If no project is specified, or the project has no routing policy, Gateway falls back to the org-level default policy.
3. No policy, direct model calls. If neither exists, Gateway routes directly to the model specified in the request.

Switching strategies per request

You cannot pass a routing strategy in the request body. To route different requests through different strategies:

1. Create one project per strategy (for example, one with Cost Optimized and another with Quality First).
2. Pass the appropriate project_id field in the request body per request. All projects share the same API key.

This is useful when different features or user tiers need different cost/quality trade-offs.

Using default_routing

Set the request’s model field to the sentinel value "default_routing" to explicitly request policy-based routing without naming a model.

The sentinel value is case-insensitive and whitespace is stripped, so " Default_Routing " resolves the same as "default_routing".

default_routing is useful when you have a client that always sends a model field, for example the OpenAI SDK or a templated request payload, but you want every request to honor the project or org default policy. Set the value once at the client level and Gateway will pick the model.

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from merge_gateway import MergeGateway
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client = MergeGateway(api_key="YOUR_API_KEY")
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response = client.responses.create(
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    model="default_routing",
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    input=[
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        {"type": "message", "role": "user", "content": "Draft a response to this support ticket."},
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    ],
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    project_id="production",
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)
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print(response.output[0].content[0].text)

FAQs