Improving the scalability of probabilistic model checking (PMC) tools is crucial to the verification of real-world system designs. The Stamina infinite-state PMC tool achieves scalability by iteratively constructing a partial state space for an unbounded continuous-time Markov chain model, where a majority of the probability mass resides. It then performs time-bounded transient PMC. It can efficiently produce an accurate probability bound to the property under verification. We present a new software architecture design and the C++ implementation of the Stamina 2.0 algorithm, integrated with the Storm model checker. This open-source Stamina implementation offers a high degree of modularity and provides significant optimizations to the Stamina 2.0 algorithm. Performance improvements are demonstrated on multiple challenging benchmark examples, including hazard analysis of infinite-state combinational genetic circuits, over the previous Stamina implementation. Additionally, its design allows for future customizations and optimizations to the Stamina algorithm.