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Credit Without Ground Truth: Auditing Step-Level Credit Assignment in LLM Agents Against Executed Replay

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TL;DR - An executed-replay audit in ALFWorld finds that common step-level credit signals for training LLM agents identify causally important actions no better than chance. This challenges correctness-based credit evaluations and shows that training comparisons must control for effective sample size.

  • Causal contribution was sparse: only 30.5% of measurable decision points affected outcomes.
  • LLM judges, outcome-conditioned log-probability ratios, and policy confidence failed to recover causally pivotal steps above chance.
  • Implicit credit primarily tracked policy fluency, while outcome conditioning added essentially no causal information.
  • Across seven training arms, none reliably beat the untrained policy; apparent differences were explained by training dose rather than credit quality.

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Credit Without Ground Truth: Auditing Step-Level Credit Assignment in LLM Agents Against Executed Replay

arXiv cs.LG Haiyue Zhang 2026-08-20 arXiv:2608.19760
Public signals Semantic Scholar citations 2 · Semantic Scholar influential citations 0
Providers: Hugging Face · N/A OpenAlex · N/A Publisher · N/A Semantic Scholar · Citations 2 · Influential citations 0 X · N/A Fetched 2026-09-19 14:25:40.726180 UTC

TL;DR - An executed-replay audit in ALFWorld finds that common step-level credit signals for training LLM agents identify causally important actions no better than chance. This challenges correctness-based credit evaluations and shows that training comparisons must control for effective sample size.

  • Causal contribution was sparse: only 30.5% of measurable decision points affected outcomes.
  • LLM judges, outcome-conditioned log-probability ratios, and policy confidence failed to recover causally pivotal steps above chance.
  • Implicit credit primarily tracked policy fluency, while outcome conditioning added essentially no causal information.
  • Across seven training arms, none reliably beat the untrained policy; apparent differences were explained by training dose rather than credit quality.
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