Claude 3.5 Sonnet Scores Just 21% on Brutal AI Research Replication Test

If you want to know how far AI agents really are from replacing PhD-level machine learning researchers, a new benchmark has a sobering number for you: 21%. That’s the top score achieved by Anthropic’s Claude 3.5 Sonnet on PaperBench, an exceptionally rigorous new test that demands agents replicate entire research papers from scratch.

The benchmark, open-sourced by its creators, doesn’t mess around with toy problems. It compiles 20 papers accepted as Spotlight or Oral presentations at the prestigious ICML 2024 conference. To fully replicate one, an agent must digest the paper’s core contributions, build a complete codebase from the ground up, and execute the experiments necessary to reproduce the reported results. This isn’t about answering multiple-choice questions; it’s about doing the job.

Scoring such a complex, long-horizon task required a novel approach. The team worked directly with the original authors of each ICML paper to co-develop hierarchical rubrics. These granular scoring guides break down every replication into thousands of smaller, verifiable sub-tasks. The entire benchmark hinges on a staggering 8,316 individually gradable tasks, all designed for objective evaluation. To manage this scale, the researchers also built an LLM-based automated judge, creating a separate benchmark just to validate the judge’s own accuracy to ensure reliable grading.

When pitted against this gauntlet, frontier models stumbled hard. Even the best-performing system, Claude 3.5 Sonnet equipped with open-source scaffolding to manage its environment and tools, could only nail about a fifth of the required work. To set a human baseline, the authors recruited top-tier machine learning PhDs to tackle a subset of the papers. The models, it turns out, couldn’t beat them. That gap highlights just how much tacit knowledge, iterative debugging, and experimental intuition remains uncaptured by current AI engineering pipelines, leaving a wide chasm between an impressive demo and true scientific labor.