auto-sklearn is an automated machine learning library offering a scikit-learn-compatible interface for classification and regression. It performs hyperparameter optimization via Bayesian optimization (SMAC), integrates meta-learning to warm-start the search from prior runs, and builds ensembles using Caruana's ensemble selection. The codebase is modular: pipeline components (classifiers, regressors, preprocessors) are defined with ConfigSpace and can be extended via a third-party component system. Parallel execution uses dask, and custom metrics, cross-validation splitters, and early stopping are supported. The repository also contains a substantial research component—precomputed meta-features and algorithm run data stored in ARFF format—and scripts for reproducing experiments. The architecture is well-tested with a comprehensive test suite, though some dependencies are pinned to older versions and there is moderate technical drift.