---
id: nnunetv2
version: "2.8.1"
license: Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. Definitions. "License" shall mean the terms and conditions for… (full text in the JSON record)
license_treatment: permissive
maintenance: active
---

# nnunetv2 — nnU-Net is a framework for out-of-the box image segmentation.

License: permissive · Maintenance: active · Downloads: 155.3K/mo

## What it is and what it does

nnU-Net is a self-configuring deep learning framework for semantic segmentation, primarily designed for biomedical image analysis. It analyzes your training data to create a dataset fingerprint, automatically selects and configures appropriate U-Net architectures (including 2D, 3D, and cascade variants), and handles the full pipeline from preprocessing through training to model selection and inference. The framework is built on PyTorch and depends on a substantial stack of scientific libraries including scipy, scikit-learn, SimpleITK, nibabel, and others for image I/O, processing, and visualization.

It works particularly well in training-from-scratch scenarios on biomedical, medical imaging, and challenge datasets where standard pretrained models are often a poor fit. While primarily designed for supervised segmentation tasks, it serves as both a production tool and a development framework for researchers exploring new segmentation methods. The package is actively maintained by the Applied Computer Vision Lab at Helmholtz Imaging and the Division of Medical Image Computing at the German Cancer Research Center.

Use it for:

- Segment organs, tumors, or anatomical structures in CT, MRI, or other medical imaging modalities without manual architecture design
- Establish a strong baseline for new segmentation datasets or medical imaging challenges
- Train and compare multiple U-Net configurations automatically on your own biomedical image data
- Preprocess and standardize medical imaging datasets for downstream analysis or model development
- Perform 3D volumetric segmentation on stacked 2D slices or native 3D imaging data

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

nnU-Net is a semantic segmentation framework that automatically configures U-Net variants based on dataset characteristics and provides end-to-end workflows for preprocessing, training, model selection, and inference on 2D and 3D images.

Yes. nnU-Net is actively maintained, has low install friction, carries a permissive Apache 2.0 license, and reports no known vulnerabilities. It is well-suited for anyone working on biomedical image segmentation who wants to avoid manual architecture tuning. The substantial dependency footprint (22 runtime packages) is appropriate for its domain and is unlikely to conflict with typical scientific Python workflows. Start with the installation and getting-started documentation.

## Install

pip install nnunetv2
uv add nnunetv2
poetry add nnunetv2

## Installing nnunetv2

Before you install: Low friction installation with a pure Python wheel. Active maintenance with a recent release 44 days ago and ongoing repository activity. Requires torch and 22 runtime dependencies including scipy, scikit-learn, and medical imaging libraries like SimpleITK and nibabel.

License in practice: Apache License 2.0 is permissive: you can use, modify, and distribute nnU-Net freely in commercial and private projects, provided you include the license and attribute the original copyright holders.

Quickstart:

pip install nnunetv2

from nnunetv2.imageio.base_reader_writer import BaseReaderWriter
from nnunetv2.training.nnUNetTrainer.nnUNetTrainer import nnUNetTrainer

Requires PyTorch to be installed first for your hardware (CPU/GPU). Requires Python >= 3.10. Needs environment setup for nnUNet_raw, nnUNet_preprocessed, and nnUNet_results directories per documentation.

Verify before relying:

- Whether the framework supports inference on pre-trained models from external sources or only on models trained within nnU-Net
- Performance characteristics and memory requirements for typical biomedical datasets
- Specific GPU/CUDA version compatibility beyond the Python requirement

## Package facts

- License: Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. Definitions. "License" shall mean the terms and conditions for… (full text in the JSON record) (permissive)
- Python support: supports_current
- Install friction: low
- Maintenance: active
- Downloads: 155.3K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

medical image segmentation, semantic segmentation framework, biomedical image analysis, automatic u-net configuration, deep learning segmentation, 3d image segmentation, self-configuring segmentation, medical-imaging, semantic-segmentation, deep-learning

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