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chimeraboost

Lightning-fast Gradient Boosting, near-CatBoost quality, all in Python

📖 Documentation: bbstats.github.io/chimeraboost

chimeraboost logo

Install

pip install chimeraboost

[OPTIONAL]:

chimeraboost-warmup

chimeraboost-warmup compiles the numba kernels once and caches them, so the first fit is not several seconds slower than the rest. Re-run it after every upgrade, which resets the cache. See Deployment.

Quickstart

from chimeraboost import ChimeraBoostClassifier, ChimeraBoostRegressor

# classification. quality picks the speed/accuracy trade-off: 1 fastest .. 5 strongest,
# defaulting to 3.
clf = ChimeraBoostClassifier(quality=5)
clf.fit(X, y, cat_features=[0, 1], sample_weight=w)
proba = clf.predict_proba(X_test)

# regression (RMSE, MAE, Quantile, Huber, Poisson, Gamma, Tweedie, or your own)
reg = ChimeraBoostRegressor(loss="Quantile", alpha=0.9)
reg.fit(X, y)

What it is

An opinionated GBDT library that only depends on common Python libraries (NumPy, numba, scikit-learn, SciPy):

  • Regression, quantile regression, binary and multiclass classification

What makes it different?

  • Bagging as a first-class feature (n_ensembles)
  • Automatic early stopping
  • Fast multi-quantile fitting (ChimeraBoostQuantileRegressor)
  • Automatic linear-leaf auditioning
  • Exact SHAP explanations (model.shap_values(X)).

Average rank vs fit-time slowdown on the public suite

Scored against CatBoost and LightGBM only; how the suite is built and weighted is in docs/benchmarks.md. On the sealed TabArena leaderboard the default scores above XGBoost and LightGBM while training faster than either; CatBoost scores higher and takes considerably longer (chart).

Documentation

  • Getting started: install and first models
  • Recipes: categoricals, quantiles, bagging, custom losses, and more
  • Parameters: every option, with defaults and guidance
  • FAQ: common questions

Why?

  • I want to be able to modify my GBDT library at will
  • I know Python and I don't know C

Inspirations / Citations

  • CatBoost, Prokhorenkova et al., NeurIPS 2018. Ordered boosting, ordered target statistics, oblivious trees.
  • XGBoost, Chen & Guestrin, KDD 2016. Regularized objective, Newton leaf estimation, column subsampling.
  • LightGBM, Ke et al., NeurIPS 2017. Histogram-based split finding.
  • Linear-leaf trees, Shi et al., IJCAI 2019 (arXiv:1802.05640). Piece-wise-linear regression trees (linear_leaves).
  • TreeSHAP, Lundberg et al., Nature Machine Intelligence 2020 (orig. SHAP, NeurIPS 2017). Exact additive feature attributions (shap_values).
  • OpenFE, Zhang et al., ICML 2023 (arXiv:2211.12507). Automated pairwise feature generation (cross_features).
  • Conformalized quantile regression, Romano, Patterson & Candès, NeurIPS 2019. Distribution-free interval calibration (conformalize).
  • TabArena, Erickson et al., NeurIPS 2025 (arXiv:2506.16791). The tabular benchmark used for evaluation.

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