---
language:
- dna
library_name: transformers
tags:
- DNA
- BERT
- language-model
- genomics
license: mit
---

# DNABERT-2

Weights and tokenizer for [DNABERT-2](https://arxiv.org/abs/2306.15006)
(Zhou et al., arXiv 2023), loaded with the shared MosaicBERT implementation
from [Taykhoom/MosaicBERT-updated](https://huggingface.co/Taykhoom/MosaicBERT-updated).

DNABERT-2 is a foundation model trained on large-scale multi-species genome data.
It replaces k-mer tokenization with Byte Pair Encoding (BPE), uses ALiBi positional
biases instead of learned embeddings, and incorporates a GLU-based FFN for improved
efficiency.

**This repo contains only weights and tokenizer files.** The model code is loaded
automatically from `Taykhoom/MosaicBERT-updated` via `trust_remote_code=True`.

## Architecture

| Parameter | Value |
|---|---|
| Layers | 12 |
| Attention heads | 12 |
| Embedding dimension | 768 |
| Intermediate size | 3072 |
| Vocabulary size | 4096 (BPE) |
| Positional encoding | ALiBi (no hard length limit) |
| Max sequence length | ~10000 nt (practical; ALiBi resizes dynamically) |
| Parameters | ~117M |

### Tokenization

Uses Byte Pair Encoding (BPE) tokenization via `PreTrainedTokenizerFast`.
No k-mer pre-processing required.

## Pretraining

- **Objective:** Masked Language Modeling
- **Data:** Large-scale multi-species genome (GRCh38 and others)
- **Source checkpoint:** `pytorch_model.bin` from [zhihan1996/DNABERT-2-117M](https://huggingface.co/zhihan1996/DNABERT-2-117M)

## Parity Verification

Hidden-state representations verified identical (max abs diff = 0.00) to the original
implementation at all 13 representation levels (embedding + 12 transformer layers).
SDPA verified (max abs diff < 1e-4). Verified on GPU with PyTorch 2.7 / CUDA 12.9.

## Related Models

See the full [DNABERT collection](https://huggingface.co/collections/Taykhoom/dnabert-6a20958f8ce004ea4e985e7b).

| Model | Architecture | Notes |
|---|---|---|
| [DNABERT-3mer](https://huggingface.co/Taykhoom/DNABERT-3mer) | BERT + k-mer | k=3 |
| [DNABERT-4mer](https://huggingface.co/Taykhoom/DNABERT-4mer) | BERT + k-mer | k=4 |
| [DNABERT-5mer](https://huggingface.co/Taykhoom/DNABERT-5mer) | BERT + k-mer | k=5 |
| [DNABERT-6mer](https://huggingface.co/Taykhoom/DNABERT-6mer) | BERT + k-mer | k=6 |
| **[DNABERT-2](https://huggingface.co/Taykhoom/DNABERT2)** | **MosaicBERT + BPE + ALiBi** | **This model** |
| [DNABERT-S](https://huggingface.co/Taykhoom/DNABERT-S) | MosaicBERT + BPE + ALiBi | Species-aware contrastive fine-tune |

## Usage

### Embedding generation

```python
import torch
from transformers import AutoTokenizer, AutoModel

tokenizer = AutoTokenizer.from_pretrained("Taykhoom/DNABERT2", trust_remote_code=True)
model = AutoModel.from_pretrained("Taykhoom/DNABERT2", trust_remote_code=True)
model.eval()

sequences = ["ACGTAGCATCGGATCTATCTATCGACACTTGG", "ATCGATCGATCGATCG"]
enc = tokenizer(sequences, return_tensors="pt", padding=True)

with torch.no_grad():
    out = model(**enc)

cls_emb  = out.last_hidden_state[:, 0, :]   # (batch, 768)
mean_emb = out.last_hidden_state.mean(dim=1) # (batch, 768) -- mean pooling

# Intermediate layers
out_all = model(**enc, output_hidden_states=True)
layer6_emb = out_all.hidden_states[6]
```

### MLM logits

```python
import torch
from transformers import AutoTokenizer, AutoModelForMaskedLM

tokenizer = AutoTokenizer.from_pretrained("Taykhoom/DNABERT2", trust_remote_code=True)
model = AutoModelForMaskedLM.from_pretrained("Taykhoom/DNABERT2", trust_remote_code=True)
model.eval()

enc = tokenizer(["ACGTAGCAT[MASK]GGATCTATC"], return_tensors="pt")
with torch.no_grad():
    logits = model(**enc).logits   # (1, seq_len, 4096)
```

### Attention implementation

```python
# SDPA (default on PyTorch >= 2.0)
model = AutoModel.from_pretrained("Taykhoom/DNABERT2", trust_remote_code=True,
                                   attn_implementation="sdpa")

# Flash Attention 2
model = AutoModel.from_pretrained("Taykhoom/DNABERT2", trust_remote_code=True,
                                   attn_implementation="flash_attention_2",
                                   torch_dtype=torch.bfloat16)
```

## Implementation Notes

The original DNABERT-2 codebase uses a Triton-based flash attention implementation
(`flash_attn_triton.py`). This HF port uses
[Taykhoom/MosaicBERT-updated](https://huggingface.co/Taykhoom/MosaicBERT-updated)
which replaces it with the standard `flash-attn` package, and also adds
`attn_implementation="sdpa"` support. These were not part of the original codebase.

## Citation

```bibtex
@misc{zhou2023_dnabert2,
  title   = {{DNABERT}-2: Efficient Foundation Model and Benchmark For Multi-Species Genome},
  author  = {Zhou, Zhihan and Ji, Yanrong and Li, Weijian and Dutta, Pratik and
             Davuluri, Ramana and Liu, Han},
  year    = {2023},
  eprint  = {2306.15006},
  archivePrefix = {arXiv},
  primaryClass  = {q-bio.GN}
}
```

## Credits

Original DNABERT-2 model and code by Zhou et al.
Source: [GitHub](https://github.com/MAGICS-LAB/DNABERT_2).
The HF conversion code was authored primarily by [Claude Code](https://claude.ai/code)
and reviewed manually by Taykhoom Dalal.

## License

MIT, following the original repository.