S3AC: Shanghai AI Lab's Stabilized Actor-Critic Method for LLM Long-Chain Reasoning
Shanghai-AI-Laboratory · hf · 2026-10-27
Shanghai AI Laboratory's S3AC paper addresses limitations of critic-free RLVR methods: GRPO-style grouped rollouts waste time waiting for the slowest response and batch-statistics baselines ignore prompt difficulty. Long CoT critic training suffers from insufficient length coverage and early gradients dominated by the newly initialized critic. S3AC introduces a stabilized actor-critic method with difficulty-aware prompt sampling, improving long reasoning without grouped rollouts.
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