Please cite gpboost including its version as

Sigrist F, Gyger T, Kündig P (2021). “GPBoost: Combining Tree-Boosting with Gaussian Process and Mixed Effects Models.” R package version 1.6.0, https://github.com/fabsig/GPBoost.

Corresponding BibTeX entry:

  @Misc{sigrist2021gpboost,
    title = {GPBoost: Combining Tree-Boosting with Gaussian Process and
      Mixed Effects Models},
    author = {Fabio Sigrist and Tim Gyger and Pascal Kündig},
    note = {R package version 1.6.0},
    year = {2021},
    url = {https://github.com/fabsig/GPBoost},
  }