Model Router Implementation

Build a smart model router that selects the optimal LLM for each request.

## Available Models
{{model_options}}

## Routing Criteria
{{routing_criteria}}

## Cost Constraints
{{cost_constraints}}

Implement a routing system:

```python
class ModelRouter:
    def route(self, request: LLMRequest) -> ModelSelection:
        """
        Consider:
        - Query complexity
        - Required capabilities
        - Cost budget
        - Latency requirements
        - Model availability
        """
        pass
    
    def classify_complexity(self, query: str) -> ComplexityLevel:
        """Determine query complexity"""
        pass
    
    def estimate_cost(self, model: str, tokens: int) -> float:
        """Estimate request cost"""
        pass
```

Include:
- Classifier training data generation
- Routing rule configuration
- Fallback logic
- A/B testing for routing decisions