CLIMB encoders

Frozen encoder weights for every run in CLIMB, a controlled study of whether unsupervised pretraining on SMILES teaches a chemical language model chemistry. All arms share one architecture, tokenizer and optimizer; they differ only in the pretraining corpus and budget.

Architecture

ModernBERT, 12 layers, hidden size 512, 8 heads, ~41.4M parameters. Byte-BPE tokenizer, vocab 1000, maximum sequence length 256.

Layout

<wave>/<run>/config.json
<wave>/<run>/model.safetensors
tokenizer/tokenizer.json, tokenizer/tokenizer_config.json, tokenizer/special_tokens_map.json

<wave> is the experiment group (climb_v2_phase2, climb_v2_expA, climb_v2_expB, and others); <run> names the arm. METHODS.md in the code repository defines every arm.

Use

from transformers import AutoModel, PreTrainedTokenizerFast
from huggingface_hub import snapshot_download

path = snapshot_download("lsieben/climb-encoders",
                         allow_patterns=["climb_v2_phase2/unsup_8M/*", "tokenizer/*"])
model = AutoModel.from_pretrained(f"{path}/climb_v2_phase2/unsup_8M")
tok = PreTrainedTokenizerFast.from_pretrained(f"{path}/tokenizer")

Encoders are used frozen, mean-pooled, with a trained head. The evaluation protocol is in METHODS.md.

What is not here

Training configurations and trainer metrics logs are not published in this repository.

Code: github.com/leifsieben/CLIMB
Encoders: lsieben/climb-encoders
Results: lsieben/climb-results
Pretraining data: lsieben/climb-pretrain-data

Citation

@misc{climb2026,
  title  = {Does Pretraining Teach Chemical Language Models Chemistry?},
  author = {Sieben, Leif and Zimmermann, Yoel},
  year   = {2026},
  note   = {Preprint, arXiv},
  url    = {https://github.com/leifsieben/CLIMB}
}

License

Apache-2.0.

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