Multi-Agent LLM Pipeline for Code Writing: An Experimental Study of Writer-Reviewer Architecture

Abstract

In this paper, we develop a multi-agent pipeline-based approach for solving competitive programming problems via Large Language Models (LLMs). Specifically, we analyze the Writer-Reviewer pipeline where the Writer Agent produces Python solutions and the Reviewer Agent gives static natural language feedback. Experiments on a 96-problem AtCoder subset of LiveCodeBench involve comparing twelve pipeline setups which employ three different models (GPT-OSS-20B, Qwen3-Coder-30B-A3B-Instruct, and Qwen2.5-Coder-7B-Instruct) in various agent roles. Within this experimental setup, the review process increases the performance of GPT-OSS-20B from 87.5% to 91.7% Pass@1, with the bootstrap 95% confidence intervals overlapping, while the performance of Qwen3-Coder-30B-A3B-Instruct does not improve and the performance of Qwen2.5-Coder-7B-Instruct improves marginally from 0% to 1.0%. This may indicate that the static iterative feedback mechanism helps to further improve the performance of a strong Writer but not the performance of a weak Writer. A diagnostic audit suggests that the very low Qwen2.5-Coder-7B-Instruct scores mainly reflect structured-output compliance failures in our setup rather than standalone coding capability. Moreover, performance varies more when changing the Writer Agent than when changing the Reviewer Agent, with differences of up to 88.6 percentage points across Writers and up to 17.7 percentage points across Reviewers.