AI Agent 多模型路由网关架构设计

You are an expert AI infrastructure architect. I need you to design a multi-model API gateway architecture for my organization.

Requirements:

• Support routing requests to multiple LLM providers (OpenAI, Anthropic, Google, DeepSeek, open-source models)
• Implement intelligent load balancing with fallback chains
• Cost optimization: route based on task complexity (simple tasks → cheaper models, complex → premium)
• Rate limiting per user/team with token bucket algorithm
• Request/response caching for identical prompts
• Unified API format (OpenAI-compatible) regardless of backend provider
• Observability: latency tracking, token usage, cost dashboards
• Authentication via API keys with team-level quotas

Please provide:

1. High-level architecture diagram (describe in text/mermaid)
2. Router decision logic (how to pick which model handles a request)
3. Fallback chain configuration example
4. Cost optimization strategy with concrete model tier examples
5. Key metrics to monitor
6. Sample configuration file (YAML)

Keep it practical and production-ready. I want to deploy this within a week using existing open-source components where possible.