Infrathon: Benchmarking Language Agents for Real-World, Long-Horizon AI Infra Optimization
Abstract
In this work, we study whether frontier agent can continually improve real-world AI infrastructure over long horizons. We introduce Infrathon, a benchmark of diverse, long-horizon AI infrastructure optimization tasks across different levels. We evaluate six models across 150 runs with 24-hour budgets, totaling over 10,000 GPU-hours. Our results show that model rankings vary with the evaluation horizon, while 135 of the 150 runs achieve further improvements during the second half of their budgets. These findings indicate that shorter evaluations can overlook both optimization gains and changes in relative model performance. We also find agents can discover solutions that outperform human-designed baselines: Claude Opus 5.5 increases the mean KV-cache compression ratio from 6.82% with the human-designed Quant-VideoGen codec to 19.86%. Analysis of agent trajectories identifies task violations, unreliable testing, and premature completion as barriers to sustained improvement. Together, Our Infrathon framework provide resources for constructing long-horizon tasks, evaluating frontier agents, and discovering good infrastructure solutions.
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Infrathon: Benchmarking Language Agents for Real-World, Long-Horizon AI Infra Optimization
Zhengyu Hu1 Zheyuan Xiao1 Yike Wang1,2 Hamish Ivison1 Haoyu Wang3 Yige Yuan1 Rulin Shao1 Yuetai Li1 Niqi Lyu4 Yicheng Ding4* Shu Yang5 Zhichen Zeng1,6 Banghua Zhu1,6 Jiaxin Pei5,7 Kaize Ding8 Pradeep Dasigi2 Dan Roth3 Hannaneh Hajishirzi1 Noah A. Smith1,2 Teng Xiao1,2*† Radha Poovendran1*
1University of Washington 2Allen Institute for AI 3University of Pennsylvania 4Pyromind Dynamics 5Stanford University 6RadixArk 7The University of Texas at Austin 8Northwestern University
†Project leader *Corresponding authors
Can frontier agents keep improving real AI infrastructure for 24 hours? Infrathon gives an agent an H100 workstation, a real ML system and a 12–24 hour budget: 25 tasks from GPU operators to full training and serving systems, scored by an independent Judge on held-out workloads. We evaluate 6 models over 150 runs and 10,000+ GPU-hours; 135 of the 150 runs still improve in the second half of their budget.
🏠 Homepage · 📝 Blog · 💻 Code · 🛠️ Infrathon-build · 🤗 Dataset · 🐳 Docker Hub
| Model | Mean rank score ↑ | Tasks won |
|---|---|---|
| Claude Opus 5.5 | 91.2 | 17 |
| GPT-6 Astra | 75.2 | 6 |
| GPT-6.1 Sol | 54.4 | 1 |
| Qwen 3.8 Flash | 40.8 | 1 |
| DeepSeek V4.1 Flash | 30.4 | 0 |
| GLM 5.3 Flash | 8.0 | 0 |
Mean rank scores range from 0 to 100; 100 means first place on every task.
| Dataset / video model | Compression (×) ↑ | PSNR (dB) ↑ | SSIM ↑ | LPIPS ↓ |
|---|---|---|---|---|
| WorldScore HY-WorldPlay | 6.75 → 20.89 | 31.15 → 36.33 | 0.923 → 0.975 | 0.059 → 0.023 |
| MovieGen LongCat-Video | 6.88 → 18.83 | 23.67 → 26.95 | 0.836 → 0.884 | 0.126 → 0.085 |
Mean values: human codec → Claude's codec. Quality metrics use the uncompressed BF16 reference.
| Task level | Best of two / one long run | Best of four / one long run |
|---|---|---|
| Operator | 101.3% | 102.6% |
| Module | 96.5% | 96.9% |
| System | 79.4% | 77.3% |
Geometric means of task–model score ratios; 100% means equal performance at equal GPU-hours.
Everything is open: the tasks, the Work/Controller/Judge images, the held-out data, and 🛠️ Infrathon-build for turning an expert's task definition into a new Infrathon task.
📄 If you find Infrathon useful, please cite:
@inproceedings{Hu2026InfrathonBL,
title={Infrathon: Benchmarking Language Agents for Real-World, Long-Horizon AI Infra Optimization},
author={Zhengyu Hu and Zhe-Yuan Xiao and Yike Wang and Hamish Ivison and Hao-Yu Wang and Yi-Ge Yuan and Ru-Lin Shao and Yue-Tai Li and Niqi Lyu and Yi-Cheng Ding and Shu Yang and Zhi-Chen Zeng and Bang-Hua Zhu and Jia-Xin Pei and Kai-Ze Ding and Pradeep Dasigi and Dan Roth and Hanna Hajishirzi and Noah A. Smith and Teng Xiao and Radha Poovendran},
year={2026},
url={https://api.semanticscholar.org/CorpusID:295731967}
}
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Rankings changing with the evaluation horizon is the finding I keep thinking about: a model that looks fine after an hour may not after twenty-four. 135 of 150 runs still improving in the second half is striking too. Did the task violations and premature completion cluster in particular models, or show up everywhere?
We saw both behaviors across multiple models, including the top performers. Our task-violation examples involve Claude, DeepSeek, and GLM submitting solutions that broke task instructions. For premature completion, selected runs with GPT-6 Astra, DeepSeek, and GLM improved by another 7.3%, 14.0%, and 24.8%, respectively, after our stop hook prompted them to continue, all within the original budget.
We’ll follow up with more detailed, systematic statistics on how often these behaviors occur in each model.
What stood out was that agents could declare completion while substantial improvements were still possible, even with time remaining.
Thank you for raising this question!
Good work.
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