README.md

---
library_name: transformers
license: "mit"
tags:
  - protein-language-model
  - fastplms
---

<!-- Generated from src/fastplms/models.toml. Do not edit. -->

# ESMFold2-Fast

## Model overview

`Synthyra/ESMFold2-Fast` packages the `biohub/ESMFold2-Fast` checkpoint with
the FastPLMs runtime for Hugging Face Transformers. It accepts raw amino-acid
sequences or typed molecular-complex specifications; low-level forward accepts
prepared feature tensors.

The repository uses the standard Transformers loading interface with
`trust_remote_code=True`. See Technical details for each registered class and
whether its weights come from the checkpoint.

The sequence- and token-classification classes reuse the pretrained backbone,
but their task heads are newly initialized. Fine-tune those heads before
interpreting their logits as predictions.

## Install and platform requirements

Install the direct dependencies published with this model:

```bash
python -m pip install -r \
  "https://huggingface.co/Synthyra/ESMFold2-Fast/resolve/main/requirements.txt"
```

The FastPLMs implementation itself is embedded in the model repository.
Transformers loads it through `trust_remote_code=True`.

This model requires Python 3.11-3.14, PyTorch 2.13, and Transformers 5.13.

The artifact requirements include the structure dependencies.

The release contract requires a CUDA device. The current validated target is
the exact NVIDIA GH200 on Linux aarch64. Linux x86-64, CPU-only, Windows, and
macOS structure runs are not release evidence.

The Hub quick start needs network access for the first download. For an
air-gapped run, build the manifest-pinned local artifact first and use the
offline example.

## Quick start

```python
from transformers import AutoModel

model_id = "Synthyra/ESMFold2-Fast"
model = AutoModel.from_pretrained(
    model_id,
    trust_remote_code=True,
    attn_implementation="sdpa",
).eval()
```

For offline validation, replace `model_id` with the manifest-built
`dist/hub/ESMFold2-Fast` path. Pass `local_files_only=True`.

## Attention backends

The quick start uses `sdpa`.

Available backends are `eager`, `sdpa`, `flex_attention`. Requesting an
unavailable backend raises instead of silently changing implementation.

`output_attentions=True` can use the documented one-call eager fallback to
materialize attention tensors. The configured backend does not change.

## Downstream prediction

The sequence and token prediction AutoClasses use the checkpoint backbone and
create a new, untrained `classifier`. Sequence labels have shape `(b,)`.
Residue labels have shape `(b, l)` and use `-100` outside biological positions.
The folding trunk is skipped. The classifier uses the checkpoint's learned pLM
state mixture and projection, followed by one trainable transformer probe.

```python
import torch
from transformers import (
    AutoModelForSequenceClassification,
    AutoModelForTokenClassification,
)

model_id = "Synthyra/ESMFold2-Fast"
sequence_model = AutoModelForSequenceClassification.from_pretrained(
    model_id, num_labels=2, trust_remote_code=True
).eval()
token_model = AutoModelForTokenClassification.from_pretrained(
    model_id, num_labels=3, trust_remote_code=True
).eval()
sequences = ["MSTNPKPQRKTKRNT", "MKTIIALSYIFCLVFA"]
batch = sequence_model.prepare_classifier_inputs(sequences)
biological = batch["attention_mask"].bool()

sequence_labels = torch.zeros(len(sequences), dtype=torch.long)
token_labels = torch.full_like(batch["input_ids"], -100)
token_labels[biological] = 0

with torch.inference_mode():
    sequence_output = sequence_model(**batch, labels=sequence_labels)
    token_output = token_model(**batch, labels=token_labels)
print(sequence_output.logits.shape)  # (b, 2)
print(token_output.logits.shape)     # (b, l, 3)
```

## PEFT fine-tuning

Install the training dependencies. Then attach LoRA to the loaded checkpoint:

```bash
python -m pip install "datasets>=4.8,<5" "peft>=0.19,<0.20"
```

```python
from peft import LoraConfig, TaskType, get_peft_model

peft_model = get_peft_model(
    sequence_model,
    LoraConfig(
        task_type=TaskType.SEQ_CLS,
        r=8,
        lora_alpha=16,
        target_modules="all-linear",
        modules_to_save=["classifier"],
    ),
)
```

This checkpoint advertises a classification head. Save the separately trained
`classifier` with the adapter.
All FastPLMs checkpoints follow the Transformers `PreTrainedModel` contract and
can use PEFT. The ESM2-specific shipped CLI is an example, not a
support boundary. Record the target modules, base revision, data identity, and
trainable parameter scope.

## Alignment-conditioning contract

This 24-block Fast checkpoint is optimized for single-sequence inference. It
was trained without MSA conditioning. It rejects `ProteinInput.msa` and low-level
MSA-derived features. Typed multichain and multimolecule inputs remain supported
when every protein chain uses `msa=None`. Use the full ESMFold2 checkpoint for
MSA-conditioned inference. This follows the official Biohub architecture
description in [Appendix A.2.1](https://biohub.ai/papers/esm_protein.pdf).


## Protein folding

The single-protein helper returns typed structure and confidence outputs:

```python
result = model.fold_protein(
    "MSTNPKPQRKTKRNT",
    num_loops=1,
    num_sampling_steps=200,
    num_diffusion_samples=1,
    seed=7,
)
pdb_text = model.result_to_pdb(result)
cif_text = model.result_to_cif(result)
print(result.ptm, result.plddt.mean().item())
```

No target structure is required. For complexes, construct the input from the
types exposed by the loaded artifact:

```python
types = model.input_types
complex_input = types.StructurePredictionInput(
    sequences=[
        types.ProteinInput(id="A", sequence="MSTNPKPQRKTKRNT"),
        types.ProteinInput(id="B", sequence="MKTIIALSYIFCLVFA"),
        types.DNAInput(id="C", sequence="ATGC"),
        types.LigandInput(id="L", smiles="O"),
    ]
)
complex_result = model.fold(
    complex_input,
    num_loops=1,
    num_sampling_steps=200,
    seed=7,
)
print(complex_result.ptm, complex_result.plddt.mean().item())
```

The typed interface also supports RNA, modifications, and covalent bonds.
Protein MSA inputs are not supported by this Fast checkpoint; every protein
chain must use `msa=None`. The public schema recognizes `PocketConditioning` and
`DistogramConditioning`, but the pinned official forward consumes neither. Its
feature builder hard-codes a zero pocket feature and constructs distogram tensors
that the released model ignores. FastPLMs therefore rejects non-null pocket and
distogram conditioning instead of silently ignoring scientific inputs. Prepared
`ref_pos` values are component reference geometries created during featurization,
not target coordinates.
Predicted coordinates and confidence scores are outputs and do not establish
biochemical activity.

## Learned representation and ESMC precision

ESMFold2 applies its learned state mixture and projection as
`H: (b, l, 81, 2560) -> Z: (b, l, 256)`. Retrieve `Z` through the public
embedding API:

```python
representations = model.embed_dataset(
    ["MSTNPKPQRKTKRNT", "MKTIIALSYIFCLVFA"],
    batch_size=2,
    full_embeddings=True,
)
print(representations[0].tensor.shape)  # (sequence_length, 256)
```

`model.embed_dataset(..., full_embeddings=True)` returns one `(l, 256)` residue
tensor per single-chain input. It rejects complexes, ligands, MSAs,
chain-separated inputs, `cls`, and `parti` in the embedding path.

Set `esmc_precision` to `auto`, `bf16`, `fp32`, or `fp8` when loading.
`auto` always resolves to BF16. Explicit FP8 is experimental, inference-only,
and strict:

```python
model.reload_esmc(precision="fp8", device="cuda:0")
print(model.esmc_precision_status)
```

FP8 raises when the validated CUDA and Transformer Engine path is unavailable.
Canonical BF16 weights are retained, and transient quantization state is never
serialized.

The ESMC backbone uses SDPA as the recommended highest-fidelity path. Flex
Attention is supported and non-experimental but can be numerically divergent;
ESMFold2 does not advertise FlashAttention for the folding interface.

| Backend | Support | Measurement status |
| --- | --- | --- |
| `sdpa` | Recommended fidelity path | Pending release measurement |
| `eager` | Supported | Pending release measurement |
| `flex_attention` | Supported, numerically divergent | Pending release measurement |

Detailed backend measurements, release guardrails, and the GH200 package
compatibility exception are maintained in the
[attention backend guide](https://github.com/Synthyra/FastPLMs/blob/main/docs/attention_backends.md)
and
[release evidence manifest](https://github.com/Synthyra/FastPLMs/blob/main/docs/generated/capability_evidence.md).


## Verified CCD runtime asset

Structure preparation requires `ccd.pkl` from
`biohub/ESMFold2`. The manifest pins its repository, revision, size, content
identity, and MIT terms. This is a trusted-deserialization boundary. FastPLMs
accepts only the pinned snapshot link inside the repository blob directory.
User-supplied asset and `cache_dir` symlinks are rejected. The loader verifies a
private temporary snapshot before deserialization, protecting against
path-replacement and in-place source-write races. Offline execution requires the
exact cached object and never downloads a replacement.

## Optional folding TTT

The standard and Fast checkpoints expose opt-in folding TTT on their ESMC
backbone:

```python
adapted = model.fold_protein_ttt(
    "MSTNPKPQRKTKRNT",
    num_loops=1,
    num_sampling_steps=50,
    seed=7,
    ttt_config={"steps": 3, "batch_size": 1, "seed": 7},
)
print(adapted.ttt_metrics)
```

Entering a gradient-enabled path reloads canonical BF16 ESMC weights. TTT adds
latency and memory and can worsen a prediction. It does not calibrate confidence
or show biological validity. Folding TTT is result-scoped. Its transient ESMC
adapter modules are excluded from checkpoint state. It is not a generic
`save_pretrained` adapter-persistence path.

## Technical details

- Inputs: Raw amino-acid sequences or typed molecular-complex specifications; low-level forward accepts prepared feature tensors
- Transformers classes: `AutoConfig`, `AutoModel`, `AutoModelForSequenceClassification`, `AutoModelForTokenClassification`
- Checkpoint weights: `AutoConfig` = `FastPLMs extension`, `AutoModel` = `pretrained`, `AutoModelForSequenceClassification` = `base weights + untrained task head`, `AutoModelForTokenClassification` = `base weights + untrained task head`
- Attention backends: `eager`, `sdpa`, `flex_attention`
- Precision: `auto`, `fp32`, `bf16`, `fp8` (experimental)
- BF16 execution: `fp32_parameters_autocast`
- Generation contract: `not_applicable`
- Dependencies: `core + structure`
- Weight publication allowed: `true`
- Weight license status: `resolved`
- Redistributable: `true`
- Complete weight publication required: `false`

## Validation and provenance

FastPLMs pins the checkpoint, upstream source revisions, state transformation,
and required files in `models.toml`. Built artifacts record exact source
identities and conversion details in `source-record.json`.

- FastPLMs checkpoint: `Synthyra/ESMFold2-Fast`
- Runtime revision: recorded separately in the built artifact and published commit
- Runtime source identities: recorded in `source-record.json`
- Official checkpoint: `biohub/ESMFold2-Fast`
- Artifact source: `fast`
- State transform: `identity`
- Pinned upstreams: `biohub-esm`, `biohub-transformers`, `protein-ttt`
- Release tiers: `check`, `compliance`, `structure`, `feature`, `artifact`, `benchmark`
- Unresolved required file identities: `0`

Release validation includes the `compliance` tier. Its evidence identifies the
checkpoint, backend, dtype, hardware, inputs, and reference revision.

Declared tiers compare configuration, tokenizer behavior, state, and
representative inference with the pinned reference. A nonzero unresolved count
blocks release. Metadata alone does not show that a build passed, that a backend
is faster, or that an output is biologically valid.

## License

Checkpoint terms: MIT. The Hub model-card identifier is
`mit`. The local artifact contains applicable source
licenses, notices, attribution, and conversion records. Review them before use.