Supplemental Material for the Paper: Under-Approximating Expected Total Rewards in POMDPs by Alexander Bork, Joost-Pieter Katoen, and Tim Quatmann. This artifact contains the implementation for the paper "Under-Approximating Expected Total Rewards in POMDPs". Our implementation is part of the probabilistic model checker Storm. Included are the source files of Storm with the extensions we made and all required dependencies. Furthermore, we include the sources of the model checker PRISM which we used as a comparison. In addition to the tools, the artifact contains the model files we used for evaluating our implementation and scripts to replicate the experiments we conducted for the paper automatically. Furthermore, we include scripts to run a subset of the experiments for a less time intensive evaluation of the implementation. For validation of our original experiments, the original logfiles are also included. The artifact has been tested to work with the TACAS 22 Artifact Evaluation VM running Ubuntu 20.04 LTS