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AIBuildAI-2.5: Efficient Autonomous AI Model Development Through LLM-Guided Tree Search

Summary

The paper introduces AIBuildAI-2.5, an agentic system that performs tree search with LLM agents. It replaces ranking by executed rewards with an LLM judge-and-selector scheme, adds a resource-aware job scheduler, and routes sub-tasks across models of different cost to cut inference spend. It ranks first on MLE-Bench with a 73.3% medal rate and beats a strong baseline on six AIRS-Bench autonomous research tasks.

SourcearXiv Computational LinguisticsAuthor: Peijia Qin, Ruiyi Zhang, Qi Cao, Han Guo, Li Zhang, Pengtao Xie
AIBuildAI-2.5: Efficient Autonomous AI Model Development Through LLM-Guided Tree Search
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[Submitted on 6 Sep 2026]

Title:AIBuildAI-2.5: Efficient Autonomous AI Model Development Through LLM-Guided Tree Search

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Abstract:Autonomous agents that automatically build artificial intelligence (AI) models could broaden access to AI across science and engineering. A popular line of such agents frames model building as a code search problem and solves it by tree search, in which each node is a candidate program and the tree grows by generating a child program from a parent, and these agents now approach the capability of experienced AI engineers on realistic benchmarks. However, these agents have three weaknesses in efficiency that have not been fully addressed. First, only a small number of candidates can be executed within a realistic budget, so search rules that rank nodes by executed rewards, such as Monte Carlo-style tree search, rely on few and noisy scores and select the next node to explore less effectively. Second, no resource-aware strategy is used to schedule training jobs, which can lower hardware utilization and training efficiency. Third, every agent call is served by a single powerful model, which inflates inference cost. Here we introduce AIBuildAI-2.5, an agentic system that carries out the tree search with LLM agents and addresses each of the three issues. AIBuildAI-2.5 proposes a novel LLM-guided tree search, in which a judge scores each candidate on its expected improvement, grounding, and feasibility, and a selector ranks the pool of candidates from these scores and the state of the search. In addition, AIBuildAI-2.5 comprises a scheduler that launches training jobs with the current hardware resource status taken into account and a router that assigns lower-cost LLMs to less demanding tasks while reserving the most capable LLM for the most challenging sub-tasks in the AI model building workflow. AIBuildAI-2.5 ranks first on MLE-Bench with a medal rate of 73.3%, and outperforms a strong baseline on six autonomous AI research tasks from AIRS-Bench.

Subjects:

Computation and Language (cs.CL); Artificial Intelligence (cs.AI)

Cite as: arXiv:2609.25047 [cs.CL]

(or arXiv:2609.25047v1 [cs.CL] for this version)

https://doi.org/10.48550/arXiv.2609.25047

arXiv-issued DOI via DataCite

Submission history

From: Ruiyi Zhang [view email] [v1] Sun, 6 Sep 2026 02:42:23 UTC (511 KB)

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Key points

  • An LLM-guided tree search replaces reward-ranked Monte Carlo-style search: a judge scores each candidate on expected improvement, grounding, and feasibility, and a selector ranks the candidate pool using those scores plus the search state.
  • A resource-aware scheduler launches training jobs with current hardware resource status taken into account, improving hardware utilization and training efficiency.
  • A router assigns lower-cost LLMs to less demanding tasks while reserving the most capable LLM for the hardest sub-tasks, reducing inference cost.
  • AIBuildAI-2.5 ranks first on MLE-Bench with a 73.3% medal rate and outperforms a strong baseline on six autonomous AI research tasks from AIRS-Bench.

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