Coding Agent Quality Fluctuations Driven by Harness Updates, Not LLM Changes, Study Finds
A new controlled longitudinal study investigates the impact of agent harness evolution on coding agent quality, finding that quality regressions often attributed to large language models (LLMs) are actually caused by updates to the agent harness. By evaluating 35 sequential releases of the Qwen Code CLI while keeping the underlying LLM constant, the study reveals that quality fluctuations are linked to specific development patterns and architectural changes in the harness.
Why it matters: This research challenges the common assumption that LLMs are primarily responsible for coding agent regressions, highlighting the significant influence of agent harness middleware and the importance of its careful management.
Full story at: arXiv Software Engineering ↗