Retroformer: Retrospective Large Language Agents with Policy Gradient
  Optimization
Authors: name: Weiran Yao, name: Shelby Heinecke, name: Juan Carlos Niebles, name: Zhiwei Liu, name: Yihao Feng, name: Le Xue, name: Rithesh Murthy, name: Zeyuan Chen, name: Jianguo Zhang, name: Devansh Arpit, name: Ran Xu, name: Phil Mui, name: Huan Wang, name: Caiming Xiong, name: Silvio Savarese

Recent months have seen the emergence of a powerful new trend in which large
language models (LLMs) are augmented to become autonomous language agents
capable of performing objective oriented multi-step tasks on their own, rather
than merely responding to queries from human users. Most existing language
agents, however, are not optimized using environment-specific rewards. Although
some agents enable iterative refinement through verbal feedback, they do not
reason and plan in ways that are compatible with gradient-based learning from
rewards. This paper introduces a principled framework for reinforcing large
language agents by learning a retrospective model, which automatically tunes
the language agent prompts from environment feedback through policy gradient.
Specifically, our proposed agent architecture learns from rewards across
multiple environments and tasks, for fine-tuning a pre-trained language model
which refines the language agent prompt by summarizing the root cause of prior
failed attempts and proposing action plans. Experimental results on various
tasks demonstrate that the language agents improve over time and that our
approach considerably outperforms baselines that do not properly leverage
gradients from the environment. This demonstrates that using policy gradient
optimization to improve language agents, for which we believe our work is one
of the first, seems promising and can be applied to optimize other models in
the agent architecture to enhance agent performances over time.