Beyond the Stability-Exploration Dilemma: Environmental Regularization for LLM Policy Optimization
Year: 2026
Type: conference-paper
Abstract: Policy optimization (PO) for Large Language Models faces a stability-exploration trade-off, currently mediated by an action-side Policy-KL regularizer.This puts practitioners in a double bind: keeping Policy-KL constrains response behavior and consumes the action-side exploration budget, while dropping it leaves the optimization without an explicit drift control.We argue for an alternative that breaks the dilemma by moving regularization to the input side.As training progresses, the distribution over training queries induced by the current policy drifts unchecked from its pre-RL reference distribution.Concretely, Environment-Regularized Policy Optimization (ERPO) introduces a Query-KL (QKL) term that bounds this query distribution shift, together with a dataset-static reference-derived perquery weight that biases each per-query update toward queries typical under the reference.The QKL gradient flows strictly through the query likelihood; the response score function used by policy-gradient estimators does not appear in the QKL term, so QKL exerts no direct gradient pressure on the response distributionexploration is preserved.ERPO plugs into GRPO/PPO/REINFORCE-style pipelines without additional forward passes.On six mathematical reasoning benchmarks, ERPO replaces the standard Policy-KL regularizer while achieving effective control over query distribution drift, delivering stronger accuracy and substantially more stable behavior under high-temperature decoding and long-horizon training.
Language: English
Subfield: Artificial Intelligence
Field: Computer Science
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W7204201890