new doc draft

Author: PatrickFarley

articles/ai-services/openai/concepts/model-router.md

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+---
+title: Azure OpenAI model router concepts
+titleSuffix: Azure OpenAI
+description: Learn about the model router feature in Azure OpenAI Service.
+author: PatrickFarley
+ms.author: pafarley
+ms.service: azure-ai-openai
+ms.topic: conceptual 
+ms.date: 04/17/2025
+ms.custom: 
+manager: nitinme
+---
+
+# Azure OpenAI model router
+
+Azure OpenAI model router is a deployable AI chat model that automatically selects the best underlying chat model to respond to a given prompt. It uses a combination of preexisting models to provide high performance while saving on compute costs where possible.
+
+## Why use model router?
+
+Model router intelligently selects the best underlying model for a given prompt. This way, smaller and cheaper models are used when they're sufficient for the task, but larger and more expensive models are available for more complex tasks. Also, reasoning models are available for tasks that require complex reasoning, but non-reasoning models are used otherwise. Model router provides a single chat experience that combines the best features from all the underlying chat models.
+
+Model router is useful for a variety of applications. TBD
+
+
+## Versioning 
+
+Each version of model router is associated with a specific set of underlying models and their versions. This set won't change—only newer versions of model router can expose new underlying models.
+
+If you select **Auto-update** at the deployment step (see [Manage models](/azure/ai-services/openai/how-to/working-with-models?tabs=powershell#model-updates)), then your model router model will automatically update when new versions become available. When that happens, the set of underlying models will also change, and this could affect the overall performance of the model as well as costs.
+
+## Underlying models
+
+|Model router version|Underlying models (version)|
+|---|---|
+|`2025-04-15`|GPT-4.1 (`2025-04-14`)</br>GPT-4.1-mini (`2025-04-14`)</br>GPT-4.1-nano (`2025-04-14`)</br>o4-mini (`2025-04-14`) |
+
+
+## Limitations
+
+Model router doesn't process input images or audio.
+
+Global Standard region support.
+
+## Billing information
+
+When you use Azure OpenAI model router, you are only billed for the use of the underlying models as they're recruited to respond to prompts. The model router itself doesn't incur any extra charges.
+
+You can monitor the overall costs of your model router deployment in the Azure portal. TBD