Model Routing: Stop Using One Model for Everything

Running a 70B parameter model to summarize a 200-word email is wasteful. Running a 3B model to review production code is reckless. Most systems live somewhere in between — and that's where model routing comes in. It matches task complexity to model capability. The tradeoffs are real, but the savings are too. The routing problem People usually start with one model and stick with it. That works until you notice the cost, or the latency, or both. The alternative is building a router — something that decides which model handles which request. Four strategies work in practice: Capability-based — route by what the model can do Cost-aware — route by what you're willing to spend Latency-aware — route by how fast you need it Hybrid — combine them Each optimizes something different. Picking one is usually a decision about what hurts most. Capability-based routing The simplest approach. Classify the task, send it to the model that handles it. Task Model size Examples Classification, tagging 1-3B Qwen2.5-1.5B, Gemma-2-2B Summarization, extraction 3-7B Qwen2.5-7B, Llama-3.1-8B Code generation 7-14B Qwen2.5-Coder-7B, DeepSeek-Coder-V2 Complex reasoning 14-32B Qwen2.5-32B, Llama-3.1-70B Creative writing, analysis 32B+ Qwen2.5-72B, Claude, GPT-4 If the task doesn't need the bigger model, don't use it. A 1.5B model handles sentiment classification fine. It just won't write a coherent essay. Implementation is straightforward: ROUTING_RULES = { " classify " : { " model " : " qwen2.5-1.5b " , " max_tokens " : 100 }, " summarize " : { " model " : " qwen2.5-7b " , " max_tokens " : 500 }, " code_review " : { " model " : " qwen2.5-coder-7b " , " max_tokens " : 2000 }, " reason " : { " model " : " qwen2.5-32b " , " max_tokens " : 4000 }, " creative " : { " model " : " claude-sonnet-4 " , " max_tokens " : 8000 }, } def route_request ( task_type : str ) -> dict : return ROUTING_RULES . get ( task_type , ROUTING_RULES [ " reason " ]) The catch is classification itself. If you get the task type