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The Automated LLM Speedrunning Benchmark: Reproducing NanoGPT Improvements

NeurIPS 2025 · Large language models › Agents, code and math · approach: Software engineering agents · 0 citations (OpenAlex)

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Introduces the Automated LLM Speedrunning Benchmark, which asks AI research agents to reproduce successive NanoGPT speedrun records given hints of varying detail, and finds that current agents recover only a small fraction of human speedups.

Problem

Whether AI research agents can faithfully reproduce sequential, code-level LLM training innovations (NanoGPT speedrun records) from descriptions of the changes.

Approach

Turns each consecutive pair of NanoGPT speedrun records into a reproduction task, scored by fraction of speedup recovered (FSR) in wall-clock training time on a fixed 8xH100 node, with four hint levels (none, pseudocode, text, mini-paper) and a flexible AIDE-based tree search scaffold.

Key results

Measured effects reported in the paper

What was changedWhereMeasuredEffect
Provide L1 pseudocode hints instead of L2 text or L3 mini-paper hintso3-mini research agents · NanoGPT speedrun record transitionsFSR: 0.40$\pm$0.02 (Flat, L1); 0.22$\pm$0.04 (Flat, L2); 0.17$\pm$0.03 (Flat, L3)Helped
Combine L1, L2, and L3 hints rather than use L1 aloneDeepSeek-R1 research agents · NanoGPT speedrun record transitionsFSR: 0.13$\pm$0.03 (Flat, L1) -> 0.30$\pm$0.04 (Flat, L1+L2+L3)Helped
Combine L1+L2+L3 hints rather than L1 aloneo3-mini + Multi-AIDE · NanoGPT speedrun record transitionsFSR: 0.43$\pm$0.02 -> 0.46$\pm$0.04Mixed
Add text and mini-paper hints to L1 pseudocodeo3-mini research agents · NanoGPT speedrun record transitionsFSR: 0.40$\pm$0.02 (Flat, L1) -> 0.24$\pm$0.05 (Flat, L1+L2+L3)Hurt
Add FlexAttention documentation to the model contextDeepSeek-R1 · Record 12 (FlexAttention)FSR: 0.09$\pm$0.01 -> 0.07$\pm$0.01Hurt
Add FlexAttention documentation to the model contexto3-mini · Record 12 (FlexAttention)FSR: 0.10$\pm$0.01 -> 0.06$\pm$0.01Hurt
Use flat best-of-M search rather than iterative search scaffoldsLLM research agents · NanoGPT speedrun record transitions with hintsFSRMixed
Use explicit debugging steps in the search scaffoldLLM research agents · NanoGPT speedrun record transitionsFSRNo clear effect
Use branching search instead of flat searchLLM research agents · NanoGPT speedrun record transitionsBuggy-node proportionHelped
Start a cumulative task from agent-generated prior code instead of ground-truth prior codeo3-mini + Multi-AIDE with L1+L2+L3 · Cumulative speedrunFSR: approximately 60%; around 20%; any speedupHurt

Surprising findings

Limitations

Experimental setup

Datasets: NanoGPT speedrun records (19 record transitions) FineWeb

Benchmarks: Automated LLM Speedrunning Benchmark

Metrics: fraction of speedup recovered (FSR) interquartile mean (IQM) L2 embedding distance recovered LLM judge reproducibility score

Baselines: MLE-bench PaperBench CORE-bench RE-bench MLAgentBench MLGym-bench AIDE

Builds on: AIDE Aider Muon NanoGPT speedrun

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