Fast Functional Generalized Estimating Equations via a One-Step Estimator R package fastFGEE version 0.1.0 Fits functional generalized estimating equations for longitudinal functional outcomes and covariates using a one-step estimator that is fast even for large cluster sizes or large numbers of clusters. The package supports quasi-likelihoods derived from a range of families, common link functions, and several working correlation structures. Uncertainty quantification is based on sandwich variance estimators and bootstrap procedures that remain valid even when the working correlation is incorrectly specified. The package provides an implementation of the method described in Loewinger et al. (2025) <https://pmc.ncbi.nlm.nih.gov/articles/PMC12306803/>. For irregularly spaced AR(1) precision matrices, the package can optionally use the archived package 'irregulAR1'; if needed, it can be obtained from the CRAN Archive at <https://cran.r-project.org/src/contrib/Archive/irregulAR1/>. Software Depends: R (>= 4.2) Imports: data.table, ggplot2, gridExtra, MASS, Matrix, mgcv, refund, Rfast, SuperGauss Suggests: irregulAR1, knitr, rmarkdown, sanic, Rcpp, RcppArmadillo Gabriel Loewinger <gloewinger@gmail.com> Comprehensive R Archive Network (CRAN) Gabriel Loewinger [aut, cre] (ORCID: <https://orcid.org/0000-0002-0755-8520>) GPL (>= 3) 2026-04-08 application/tgz https://CRAN.R-project.org/package=fastFGEE doi:10.32614/CRAN.package.fastFGEE