Why a single AI model is no longer enough
If you’re building AI-powered applications today, you’ve probably faced this problem already:
- Some prompts are trivial, but they still hit an expensive model
- Others are complex and fail badly when routed to a cheaper one
- Latency, cost, and quality constantly pull in different directions
Using one model for every prompt is increasingly inefficient especially as new models with very different strengths are released every few weeks.
This is where model routing comes in.
The hospital triage analogy
Consider a large hospital where patients arrive all day with very different problems:
- A sore throat
- Chest pain
- Sudden vision issues like floaters
Patients do not reliably know where to go. Some choose to see a consultant directly, some underplay their symptoms, while others bounce between departments losing valuable time in the process.
To handle this situation, hospitals rely on a triage lead.
The triage lead does not treat patients; they simply ensure that each patient is redirected to the right department in the hospital based on:
- Complexity of the case – simple symptom vs. unclear combination of issues
- Urgency / latency of the case – how quickly the case needs attention
- Cost and resource use – does this really require top‑tier expertise now?
- Expected performance / accuracy – does this require a specialist or advanced diagnosis?
What is model router
A model router is like that triage lead in a hospital. It intelligently routes prompts to the most suitable AI model from a collection of available models in real time rather than relying on a single model for all queries.
Simple prompts can be handled by smaller, faster, and cheaper models, while more complex reasoning can be routed to more capable models automatically.
How does a model router work?
The obvious next question that comes to mind is: how does a model router actually work?
Nowadays, models are released rapidly, and we already have benchmark datasets to compare them. It is hard to imagine that a single model will perform best across every dataset, especially when benchmarks measure very different capabilities.
As an AI developer or architect, the real interest is knowing which model performs best for a specific task or use case.
A model router is trained on various benchmark datasets to learn the relationship between prompt types and model strengths.
Large Language Model Routing with Benchmark Datasets
Model routing in cloud platforms
Cloud providers already offer out-of-the-box model routing capabilities:
- Azure AI Foundry – Model Router
- AWS Bedrock – Intelligent Prompt Router
According to Microsoft documentation:
We train the router on a large, diverse dataset spanning hundreds of thousands of examples across many domains. These include question answering, code generation, mathematical reasoning. Summarization, conversations, and agentic workflows are also covered. We continuously expand the training data to keep pace with new models and capabilities.
Open ecosystem support
OpenRouter also provides similar capabilities. It allows AI engineers to optimise model usage based on specific needs such as cost, quality, or speed, while automatically maintaining fallback strategies.
Benefits of using a model router
Based on the incoming prompt, a model router intelligently identifies and routes to the most suitable model. Smaller, less expensive models are used when they are sufficient for the task.
This leads to:
- Lower inference costs
- Reduced latency
- More efficient and sustainable compute usage
The following Microsoft community blog shares the cost benefits achieved using model routing in Azure AI Foundry:
Optimising AI costs with Microsoft Foundry Model Router
Measurable cost savings across all modes:
4.5% in Balanced, 4.7% in Cost, and 14.2% in Quality mode.
Quality mode saved the most by routing simple prompts to faster, cheaper models while still directing complex requests to more capable models.
What’s next?
In the next article, I’ll provide a step-by-step guide on how a model router can be created in Microsoft AI Foundry, covering model selection strategies, routing behaviour, and practical considerations for production systems.