MLExpert Is a Generalist Agent Built to Run Machine-Learning Engineering End to End
A 35B Mixture-of-Experts model trained with windowed interaction RL now matches frontier-scale models on autonomous ML engineering benchmarks.
The paper introduces MLExpert, a 35B Mixture-of-Experts agentic model for autonomous machine learning engineering, trained through a post-training method designed for long-horizon MLE optimization. The authors argue that feedback in MLE runs is costly and confounded: each experiment result reflects several preceding decisions, and a full run contains many such experiments. Their response is two-stage. Hierarchical agentic SFT transfers general tool-use and coding capabilities to MLE through outcome-guided supervision. Windowed Interaction RL (WIRL) then treats the multi-turn decisions between successive experiment results as an execution window and assigns it a shared outcome-based reward. Asynchronous collection and policy correction allow policy updates before a trajectory ends, addressing the credit-assignment problem across long interaction sequences.
To train the model, the authors built the Kaggle-MLE Factory, which constructs executable tasks and provides an interaction harness for model-directed experimentation. On MLE-Bench Lite, MLExpert improves the average medal rate of its base model from 37.9% to 72.7%. The paper states this is comparable to larger frontier models such as Kimi-K3 and GLM-5.3. Beyond the primary benchmark, MLExpert also improves performance on NatureBench Lite, agent scaffold optimization, and algorithm optimization, which the authors interpret as evidence that the learned optimization capability generalizes beyond the training distribution.
The contribution is less a new architecture than a training recipe for agentic MLE. The model size is modest relative to frontier systems, and the gains come from how supervision is selected from long trajectories and how intermediate outcomes are converted into rewards. WIRL is the central novelty: rather than rewarding a full run or individual actions, it rewards execution windows bounded by experiment results, which aligns reward granularity with the natural feedback cadence of ML experimentation.