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Massachusetts Institute of Technology
  • on: Oct. 20, 2026
  • in: Article

Reactive Optimizers

@misc{bai2026reactive,
    title = { Reactive Optimizers },
    author = { Bai, Xingjian and 
               Liang, Jia-Hao and 
               Teoh, Jayden and 
               Sitzmann, Vincent },
    year = { 2026 },
    booktitle = { Article },
}
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We put an LLM agent at the heart of the optimizer. It watches the training dynamics, reacts to them, and rewrites the optimizer’s source code as training goes, all within a single run. When no recipe has been tuned for a task, our system OPAL (OPtimizer with an Agent in the Loop) matches or beats the best off-the-shelf recipe across image and language tasks. The agent spontaneously discovers sophisticated schedules, such as learning-rate increases and per-module rate changes, and intricate strategies to prevent loss spikes and escape overfitting.