Model Routing: Field Notes from Twelve Months of Production

By C.W. Jameson · Published 10 February 2026 · Last reviewed 10 February 2026

The surprise: the routing classifier itself was the hardest part. The model selection, once you have the signal, is straightforward.

What I learned routing 40 million LLM calls across Haiku, Sonnet, Opus, and GPT-4o over twelve months.