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AREX-2 Advances Self-Improving Agents via Long-Horizon Reflective Tasks: Scoring 81.8 on MLE-bench and 92.2 on GAIA

Test-time self-improvement—the ability of an agent to iteratively refine solutions during inference—relies on high-fidelity reflection to surpass current proposals and long-horizon execution to maintain coherent multi-round exploration. Researchers from Renmin University of China, Microsoft Research, and USTC introduce AREX-2, establishing that these capabilities are domain-agnostic and learnable from verifiable environments. Synthesizing long-horizon reflective trajectories across machine learning and algorithmic programming, an AREX-2 agent built on Qwen3.8-27B achieves 81.8 on MLE-bench Lite and 70.7 on Frontier-CS, transferring seamlessly to deep research with 84.0 on BrowseComp, 92.2 on GAIA, and 93.8 on DeepSearchQA while monotonically scaling with compute budget.

AREX-2 Advances Self-Improving Agents via Long-Horizon Reflective Tasks: Scoring 81.8 on MLE-bench and 92.2 on GAIA

Key Takeaways

  • Identifies reflection and long-horizon execution as domain-agnostic foundations for test-time self-improving agents
  • Achieves 81.8 on MLE-bench Lite and 70.7 on Frontier-CS using an AREX-2 Qwen3.8-27B model
  • Transfers zero-shot to deep research benchmarks, scoring 92.2 on GAIA, 93.8 on DeepSearchQA, and 84.0 on BrowseComp
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AREX-2 Advances Test-Time Self-Improving Agents via Long-Horizon Reflective Programming: 81.8 on MLE-bench

Endowing LLM agents with test-time self-improvement—the ability to iteratively refine solutions—is a vital milestone for autonomous engineering. Researchers from Renmin University and collaborators present AREX-2, an open-source framework leveraging long-horizon reflective trajectories. Decoupling self-improvement into reflection (generating superior alternatives) and long-horizon execution (sustaining iteration over multiple turns), AREX-2 trains on verified machine learning and algorithmic programming trajectories. Built on Qwen3.8-27B, AREX-2 achieves 81.8 on MLE-bench Lite and 70.7 on Frontier-CS, transferring effectively to deep research with 92.2 on GAIA and 93.8 on DeepSearchQA.

AREX-2 Advances Test-Time Self-Improving Agents via Long-Horizon Reflective Programming: 81.8 on MLE-bench

Key Takeaways

  • Decouples test-time self-improvement into domain-agnostic reflection and long-horizon execution
  • Achieves 81.8 on MLE-bench Lite and 70.7 on Frontier-CS with Qwen3.8-27B, transferring to 92.2 on GAIA
  • Breaks multi-turn degradation bottlenecks, showing monotonic score improvements as iteration budgets increase
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