OpenPath is a vision foundation model for computational pathology: a ViT-g/14 encoder
pre-trained with self-supervision (DINOv2 + gram anchoring) on public-only whole-slide
histopathology tiles. This repository contains the training, reproduction, and evaluation code
plus the released weight (teacher_checkpoint.pth = training_316250). The corpus and the full
checkpoint set are hosted separately (see below).
Headline result. On AMC-HCC-ST — a contamination-free in-house Asan Medical Center
hepatocellular-carcinoma spatial-transcriptomics cohort, the least leakage-prone benchmark since no
public foundation model was trained on it — OpenPath ranks #1 among seven foundation models (mean
Pearson: OpenPath 0.323 > UNI2-h 0.301 > OpenMidnight 0.300 > Virchow2 0.292 > prov-gigapath 0.286 >
Phikon-v2 0.274 > UNI 0.257). Released checkpoint: training_316250 (in openpath-checkpoints).
See Evaluation.
Encoder: ViT-g/14 (reg4), 1536-dim CLS embedding
Objective: DINO + iBOT + KDE (DINOv2) with gram anchoring (technique from DINOv3, re-implemented)
Data: public pathology WSIs only (TCGA, TCIA, GTEx, CAMELYON, ACROBAT, SurGen, …), re-tiled at native 40×
full teacher-checkpoint set (training_0 … training_345000)
Code + weight
taejoon89/openpath
This repository — code + the released teacher_checkpoint.pth (= training_316250). Code mirror: GitHub
The training config points to the corpus via
train.sample_list_path: "openpath:glob=<corpus>/*/tiles/shards/w*/*.tar". The gram anchor
(gram.ckpt) is an earlier OpenPath teacher checkpoint from openpath-checkpoints.
Method — gram anchoring
Long self-supervised training degrades dense/patch features. Following DINOv3, we add a
gram anchoring loss: the MSE between the L2-normalized patch-token Gram (similarity) matrices
of the student and a frozen anchor model (a strong earlier checkpoint). The loss weight is 40
and it activates near the dense-feature peak (iteration 57,500) with a 3k-iter ramp. This
dampens the post-peak decline of dense representations while DINO/iBOT keep optimizing the
global representation.
1exportPYTHONPATH="$PWD/OpenPath"2CFG=OpenPath/dinov2/configs/train/openpath_vitg14.yaml
3# edit CFG: train.sample_list_path (corpus glob), gram.ckpt (anchor checkpoint), MODEL.WEIGHTS (DINOv2 warm-start)4# set your cluster (see scripts/launch.sh header): MASTER_NODE, WORKER_NODES, MASTER_ADDR, NCCL_IB_HCA, *_SOCKET_IFNAME5exportMASTER_NODE=node1 WORKER_NODES="node2 node3 node4 node5"MASTER_ADDR=<master-ib-ip>6bash scripts/launch.sh openpathrun "$CFG"<output_dir><log_dir>7# optionally run scripts/autoresume.sh (background) and scripts/watch_eval.sh (online HEST)
Extract CLS embeddings for downstream use (teacher_checkpoint.pth = the released training_316250,
included in this repo):
python
1import torch, dinov2.models.vision_transformer as vits
2ck = torch.load("teacher_checkpoint.pth", map_location="cpu", weights_only=False)3sd ={k[len("backbone."):]: v for k, v in ck["teacher"].items()if k.startswith("backbone.")}4m = vits.vit_giant2(patch_size=14, img_size=224, block_chunks=4, num_register_tokens=4,5 ffn_layer="swiglufused", init_values=1e-5,6 interpolate_antialias=True, interpolate_offset=0.0)7m.load_state_dict(sd, strict=True); m.eval()8cls = m.forward_features(x)["x_norm_clstoken"]# (B, 1536)
Evaluation
Frozen-encoder linear/ridge probing. The headline benchmark is AMC-HCC-ST — a
contamination-free in-house Asan Medical Center hepatocellular-carcinoma Visium
spatial-transcriptomics cohort (leave-one-patient-out, mean Pearson over top-50 highly-variable
genes) — no public FM was trained on it, so it is the least leakage-prone comparison. The
reported OpenPath checkpoint is training_316250.
Comparison — all 7 models loaded through one backbone factory and probed under an identical
protocol; sorted by the clean AMC-HCC-ST benchmark:
Model
AMC-HCC-ST (clean) ↓
HEST-1K (public)
NCT-CRC-HE (9-cls acc)
BACH (4-cls acc)
OpenPath
0.323
0.372
0.954
0.761
UNI2-h
0.301
0.414
0.966
0.908
OpenMidnight
0.300
0.390
0.967
0.906
Virchow2
0.292
0.398
0.964
0.875
prov-gigapath
0.286
0.393
0.953
0.752
Phikon-v2
0.274
0.375
0.937
0.708
UNI
0.257
0.386
0.946
0.777
On the contamination-free AMC-HCC-ST cohort OpenPath ranks #1 among all seven foundation models.
The picture inverts on the public benchmarks (HEST-1K, CRC, BACH): there OpenPath is mid-pack to
low, and the large FMs lead. Those benchmarks derive from public repositories (TCGA/GTEx/etc.) that
these FMs were pre-trained on, so their apparent edge is confounded by train/test leakage — which
is exactly why the leakage-free AMC-HCC-ST cohort is our headline. (The reported checkpoint
training_316250 is selected by AMC-HCC-ST; OpenPath's HEST-1K peaks earlier in training at ~0.38.)
PCam / CAMELYON is excluded because it overlaps our own training corpus.
Reproducing the comparison
All models are loaded through a single backbone-factory module (eval/openpath_eva_backbone.py) and
probed under an identical protocol, so OpenPath and the reference FMs (Phikon-v2, OpenMidnight, UNI,
UNI2-h, gigapath, Virchow2) are directly comparable.
bash
1exportPYTHONPATH="$PWD/OpenPath:$PWD/eval"2# Headline: AMC-HCC-ST (LOPO ridge; cohort is private, code is provided)3python eval/st_bench.py --backbone openpath --weights <teacher_checkpoint.pth>4python eval/st_bench.py --backbone uni # reference FM (also: uni2 / gigapath / virchow2 / phikon / openmidnight)56# Patch probing (PCam / CRC / BACH) via kaiko-eva7bash eval/run_patch_eval.sh openpath crc <teacher_checkpoint.pth>8bash eval/run_patch_eval.sh uni crc # reference FM
Reference FM weights are pulled from their Hugging Face hubs on first use (UNI / UNI2-h / Virchow2
are gated — request access on HF beforehand).
Evaluate your model on AMC-HCC-ST — we run it for you
AMC-HCC-ST is an in-house, contamination-free spatial-transcriptomics cohort that we are actively
curating and expanding at Asan Medical Center. Because it is patient-derived, the cohort cannot
be publicly redistributed. Rather than keep it as an internal-only benchmark, we offer to run the
evaluation on your behalf — send us your pathology encoder and we return its AMC-HCC-ST score under
the exact protocol used above (leave-one-patient-out ridge, top-50 HVG, mean Pearson), directly
comparable to the reference models.
What to send
Weights — a teacher_checkpoint.pth / state_dict, or a public Hugging Face / timm hub id.
A loader — a small build() returning an nn.Module that maps a normalized (B, 3, 224, 224)
batch to a (B, d) tile embedding (CLS or pooled), plus the expected input normalization
(ImageNet by default). See eval/openpath_eva_backbone.py for the exact interface we use.
Optional — a one-line model description and license so we can report your result correctly.
Every submission runs through the same single backbone-factory + probing pipeline (eval/), so your
numbers are apples-to-apples with the table above. This keeps the benchmark leakage-controlled and
open to the community even though the underlying data stays private.
Intended use. OpenPath is a frozen feature extractor for H&E histopathology. It produces a
1536-dim CLS embedding per 224×224 tile (native ~40× / 0.5 µm-per-pixel regime, ImageNet
normalization) for downstream linear/ridge probing, k-NN, MIL aggregation, and retrieval. It is a
research artifact, not a medical device, and must not be used for diagnosis or clinical
decision-making.
Limitations.
Public-benchmark leakage. Public benchmarks (HEST-1K, NCT-CRC-HE, BACH) derive from repositories
(TCGA/GTEx/…) that many foundation models — and partly OpenPath — were pre-trained on. Absolute
numbers and cross-model rankings on them are confounded; prefer leakage-controlled evaluation.
Checkpoint trade-off. The released training_316250 is selected by the clean AMC-HCC-ST benchmark;
earlier checkpoints score higher on HEST-1K (~0.38). Pick a checkpoint to match your downstream task.
Domain. Trained on H&E WSIs at native magnification. Behavior on IHC, cytology, frozen sections,
non-0.5 µm-per-pixel inputs, or non-pathology images is untested.
Patch-level encoder. OpenPath encodes tiles independently; slide-level context requires a
separate aggregator (future work).
Citation
A paper is in preparation. Until then, please cite the repository and the upstream work it builds on:
bibtex
1@misc{openpath2026,
2 title = {OpenPath: Public-Data Pathology Foundation Models and Leakage-Free Evaluation},
3 author = {Tae Joon Jun},
4 year = {2026},
5 note = {https://huggingface.co/taejoon89/openpath}
6}
OpenPath builds on DINOv2, OpenMidnight / Midnight, and gram anchoring (DINOv3) — see
OpenPath/README.md for the full upstream citations, which should also be cited.
Acknowledgements
This research was supported by a grant of the Korea Health Technology R&D Project through the Korea
Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of
Korea (grant number: HR21C0198); the Advanced GPU Utilization Support Program funded by the Government
of the Republic of Korea, Ministry of Science and ICT; and the National Research Foundation of Korea
(NRF) grant funded by the Korean government (MSIT) (grant number: RS-2026-25522634).
License
Code — Apache-2.0. This repository is a fork of DINOv2 / OpenMidnight (both Apache-2.0); see
OpenPath/LICENSE. The gram-anchoring loss (OpenPath/dinov2/loss/gram_loss.py) is a clean-room
re-implementation of the DINOv3 technique — written from its mathematical description and verified
to be numerically equivalent — so it is Apache-2.0 as well, and the codebase contains no
non-commercial (DINOv3-licensed) code.
Weights — Apache-2.0 (warm-started from Meta DINOv2 ViT-g/14-reg, itself Apache-2.0).
Training data: public pathology datasets under CC-BY / CC0 / NIH-open terms (redistributable).
