GitHub shipped HydraFusion as a research preview in Copilot, exposing the plumbing behind multi-model orchestration for coding workflows. The system routes subtasks across different LLMs based on complexity, matching Opus 5 baseline performance while reducing estimated workflow cost. This is production infrastructure for cost-quality tradeoffs, not a research paper.
The Routing Problem
Most agentic coding tools send every task to a single frontier model. You pay top-tier pricing for trivial edits and complex refactors alike. HydraFusion splits workflows into subtasks and assigns each to the cheapest model capable of solving it.
The routing layer must answer three questions:
Complexity classification: Is this task simple (renaming variables), medium (adding error handling), or hard (redesigning an API)?
