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About this paper

Wachiravit Modecrua, Krittanon Kaewtawee, Krittin Pachtrachai, Touchapon Kraisingkorn

The authors develop a reward-calibration method combining IRC with discounted, dampened outcome signals to train tool-using customer-service agents. IRC uses rollout outcomes to assign rewards to action categories, while the hybrid checks advantage directions. In this 50-task airline evaluation, Qwen3.5-4B rose from 63.8% to 66.7%, and Qwen3-30B-A3B rose from 58.0% to 69.5%.

Key insights

  • Dense per-turn rewards, when uncalibrated, can significantly degrade multi-turn agent performance due to "advantage misalignment" in advantage computation.
  • Iterative Reward Calibration (IRC) reveals that empirically calibrated rewards, sometimes setting intuitive positive rewards to zero or negative, are essential for robust learning.
  • Sparse reward training can accidentally focus gradients on critical "gold-diverse" positions due to "dead turns," which can sometimes outperform naïvely dense reward schemes.

Summary by alphaXiv.

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