How Much of a Harness Does a Strong Agent Need for Autonomous ML Engineering?

Title:How Much of a Harness Does a Strong Agent Need for Autonomous ML Engineering?

Abstract:Recent autonomous machine learning engineering (MLE) agents have made significant progress on public leaderboards. Often motivated by progress stagnation over long-horizon cycles and limited Large Language Model (LLM) primitives, modern MLE agents are deployed on top of increasingly elaborate machinery: multi-agent orchestrators, dedicated retrieval subagents, and more. While such harnesses expand, the use of more primitive but improved coding agents - where LLMs have direct access to the execution environment through read, write, and bash primitives - has received little attention in the field. In this paper we find that, under an equal time budget and the same frontier LLM backbone, open-source state-of-the-art harnesses provide no advantages over a single session of a minimal-harness coding agent baseline, pointing to the backbone as the primary driver for performance. Via a series of large-scale systematic ablation studies, we argue that the machinery layers become redundant in the coding agent setting. We conclude that the effort spent elaborating hand-crafted harnesses around strong models yields poor returns for current MLE benchmarks.

Artificial Intelligence (cs.AI)

arXiv:2609.40303 [cs.AI]

(or arXiv:2609.40303v1 [cs.AI] for this version)

https://doi.org/10.48550/arXiv.2609.40303 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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