add what's new

Author: PatrickFarley

articles/ai-services/openai/whats-new.md

@@ -21,6 +21,10 @@ This article provides a summary of the latest releases and major documentation u
 
 ## April 2025
 
+### Model router (preview)
+
+Azure OpenAI model router is a deployable AI chat model that automatically selects the best underlying chat model to respond to a given prompt. For more information on how model router works and its advantages and limitations, see the [Model router concepts guide](./concepts/model-router.md). To use model router with the Completions API, follow the [How-to guide](./concepts/model-router.md).
+
 ### o4-mini and o3 models released
 
 `o4-mini` and `o3` models are now available. These are the latest reasoning models from Azure OpenAI offering significantly enhanced reasoning, quality, and performance. For more information, see the [getting started with reasoning models page](./how-to/reasoning.md).