A Bayesian Surrogate Evaluation Test R package BSET version 1.0 An implementation of the Bayesian Surrogate Evaluation Test (BSET) for assessing the validity of surrogate markers in clinical trials. Provides hypothesis testing tools to evaluate whether a surrogate can reliably estimate the causal effect of a treatment on a primary outcome. Implements the imputation-based Bayesian methodology of Carlotti and Parast (2026) <doi:10.48550/arXiv.2603.14381>, extending the frequentist rank-based approach of Parast et al. (2024) <doi:10.1093/biomtc/ujad035>. Addresses key limitations of the frequentist method, including the lack of causal interpretability and the inability to adjust for covariates in the estimation process. Software Depends: R (>= 3.5) Imports: rstan, ggplot2, future, parallel, mvtnorm, dplyr, SurrogateRank, Rdpack, rlang Suggests: knitr, rmarkdown, bookdown, Pietro Carlotti <pietro.carlotti@utexas.edu> Comprehensive R Archive Network (CRAN) Pietro Carlotti [aut, cre], Layla Parast [aut] GPL-3 2026-05-22 application/tgz https://CRAN.R-project.org/package=BSET doi:10.32614/CRAN.package.BSET