ResearchResearch paperReasoning & Planning · Reinforcement Learning2 sources · Oct 19, 2026

HarnessRL: Co-Evolving Policies with a Just-in-Time Training Harness for Open-Ended RL

Rubric-based reinforcement learning (RL) trains policies for open-ended generation with natural-language criteria as rewards, but these rewards can become ineffective as training progresses.

Key points

  • Both reflect a training configuration whose task sampling, exploration, and evaluation stay fixed as the policy evolves.
  • We introduce HarnessRL, a training-time harness that co-evolves with the policy through three interfaces for task sampling, rollout guidance, and rubric criteria.
  • HarnessRL maintains a training-time memory from which a harness evolver retrieves within-task history and cross-task evidence.
  • Using this evidence, the evolver attributes each reward failure to the interface whose update can address it.

Sources (2)

Extractive summary: sentences quoted from the sources.

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