AC2: actor-critic with action chunking enables partial rollouts, trains faster than GRPO
ZeYanjie · x · 2026-10-03
Researchers propose Actor-Critic with Action Chunking (AC2), tackling a key question: do you really need to finish every rollout in RL for LLMs?
- Core idea: train a learned critic to score chunks of tokens — and trust it — so only partial rollouts are needed to estimate returns
- Result: faster training than GRPO, which requires full rollouts
- Significance: if it holds up, this could meaningfully cut compute costs of RL post-training
Shared via retweet by wenkaiyue, the pitch is "make your critic better — and trust it" instead of brute-force completing all samples.
Related event: AC2: Action-Chunked Actor-Critic Trains Faster Than GRPO with Less Compute(2 posts)→
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