API Gateway for LLM Services

Design an API gateway for managing multiple LLM services.

## LLM Providers
{{llm_providers}}

## Traffic Requirements
{{traffic_requirements}}

## Gateway Features
{{required_features}}

Design the gateway:

**Routing Layer**
- Provider selection logic
- Load balancing
- Failover handling

**Rate Limiting Layer**
- Per-user limits
- Per-provider limits
- Burst handling

**Authentication Layer**
- API key management
- Token validation
- Usage attribution

**Observability Layer**
- Request logging
- Metrics collection
- Cost tracking

**Transformation Layer**
- Provider API normalization
- Request/response mapping
- Streaming support

Provide:
- Architecture design
- Implementation approach
- Configuration schema
- Deployment recommendations