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Li2SAO lifts single-rollout asynchronous RL with group-relative actor-critic bootstrapping, and closes the gap with GRPO on agentic tasks

AspireAI community · arXiv (cs.LG, cs.CL)
Asynchronous reinforcement learning updates a model as rollouts arrive, but group-wise sampling fits it awkwardly because rollout lengths are long-tailed. Single-rollout Asynchronous Optimization (SAO) was proposed for that, but it depends on a closed-source value model obtained by scaling value pretraining. This paper analyses GRPO against a lightweight reproduction of SAO without that pretrained value model, and finds the ordering flips by task type: GRPO wins on reasoning tasks, while the reproduction wins on agentic ones, though it lags substantially in early training. Li2SAO fixes the cold-critic problem by training the actor on a group-relative advantage and the critic on a group-centered return until the critic is warm, then switching to single-rollout GAE. The authors report Li2SAO catching up with or surpassing GRPO in early training and raising later performance, but the headline comparison is against their own reproduction of SAO rather than the original closed-source system.
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