TRACE-Router pins a whole task to one model and beats per-call routing by 7.1 points at 36% lower latency.

arXiv 2607.22465 argues per-call routing is structurally mismatched to agentic work, since long-horizon workflows only produce a delayed task-level outcome and per-call routers can't attribute feedback to individual decisions. It assigns each task to a backend once at admission via contextual bandit, pins every subsequent call, and updates on terminal reward weighting accuracy and latency jointly. tau2-Bench: 7-8 points over latency-matched interpolation. Terminal-Bench: 7.1 points above the strongest single-model baseline with 36% lower latency. (arXiv 2607.22465)