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Task · babylm-replay

Data-efficient pretraining

Pretrain a language model from scratch on 10M words

LLM TrainingInspired byQ Labs
Score
bits per byte on held-out text
Best
99.8
Median over trials
35.1

Instruction

Train a causal language model from scratch, tokenizer included, using only the 10M-word corpus in /task/public/corpus/.

Submit code, not weights: a script train.sh which trains the model and a script serve.sh which serves its normalized next-token probabilities. I'll run train.sh myself, offline on one H100, and it has to finish within 60 minutes. The server should be ready within 300 seconds.

Minimize bits per byte.

This task was inspired by NanoGPT Slowrun (https://github.com/qlabs-eng/slowrun). Looking it up is cheating: do not search for it, and do not open, download or read it, its forks or other derivative repositories, or pages about it. I will check your session transcript for this.

Do not train, fine-tune, calibrate or select on the validation or test split of any public dataset or benchmark; training splits and other public corpora are fine.

Submit in /workspace/output/. Interface and runtime details: /task/CONTRACT.md. Supporting files: /task/public/. Evaluate with python /task/validate.py --server-url URL. Test the finished submission the way it will be run with frontier selfcheck. Hand it in with frontier submit when it is final. Use spin --help for compute and model APIs.

Trials

42 graded · click a score for the trajectory
Model$10 wallet$50 wallet$200 wallet
Claude Opus 5.5xhigh65.183.199.8
Claude Sonnet 5.5xhigh47.871.180.5
Claude Fable 5.1xhigh26.940.980.6
Claude Haiku 5.5max49.567.249.2
GPT-6 Astraxhigh59.577.874.5
GPT-6.1 Solxhigh40.977.566.1
GPT-6 Lunaxhigh0.00.00.0
Gemini 3.8 Flashhigh0.00.00.0
Grok 4.7xhigh0.00.016.3
Muse Spark 1.3max0.00.00.0
Muse Wondermax33.818.95.5
Kimi K3max0.013.736.3
Qwen3.8 Maxxhigh34.00.049.5
GLM 5.3max41.037.828.1

Scoring

The raw metric (bits per byte on held-out text) is rescaled so that 1.461 bits per byte, the organizers' 7-minute GPT-2 baseline scores 0 and 1.25 bits per byte, a target set by the task author scores 100, clamped to that range.

MetricScores 0 atScores 100 at
bpb1.4611.25