Model Routing Is Simple. Until It Isn't.
A Blog post by IBM Research on Hugging Face Back to Articles a]:hidden"> Model Routing Is Simple. Enterprise Article Published July 15, 2026 Upvote 12 +6 Yara Rizk yarizk Follow ibm-research Eyal Shnarch eishna Follow ibm-research Jason Tsay jsntsay Follow ibm-research Merve Unuvar mrvnvr Follow ibm-research Building a router into your agent sounds like an easy win. Send simple requests to cheaper models, reserve expensive ones for harder tasks, or route by specialty - Claude for code, Gemini for multimodal, and so on.
Key Takeaways
- A classifier or heuristic makes the call, costs go down, performance stays up.
Most routing systems assume that model selection is a classification problem.
- Caching - something most routing discussions ignore entirely.
Agent workloads tend to reuse large chunks of context across steps.
- First, difficulty is often invisible at routing time.
A request like "summarize this contract" looks simple, but might trigger retrieval, compliance checks, tool use, and multiple rounds of refinement before it's done.
- Routers aren't solving one problem.
They're constantly juggling cost, quality, latency, compliance, and reliability all at once.
- But routing at every step - which gives you more flexibility to adapt mid-execution - means every additional decision point introduces latency and operational complexity.
A classifier or heuristic makes the call, costs go down, performance stays up. Most routing systems assume that model selection is a classification problem. In our experience building routing into agentic systems, what looks like a model-selection problem quickly becomes a systems optimization problem.
Three dimensions made this surprisingly hard for us. Cost Is More Than Model Pricing We expected GPT-4. 1 to be cheaper than Claude Sonnet 4.
Across 417 tasks on the AppWorld Test Challenge using the same CodeAct agent, Sonnet cost $79 total ($0. 1's token pricing is lower on both input and output, and Sonnet takes roughly three times as many reasoning steps to finish the same tasks. Caching - something most routing discussions ignore entirely.
For more details please read the original article at Hugging Face.
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