This study presents a predictive transient model developed for simulating experiments at the Transient Reactor Test (TREAT) Facility and its application to the Sirius-2c experiments. We introduce an innovative approach to predict control rod motion, reactor power, and specimen temperature during transient experiments using Griffin, BISON, and the stochastic tool packages of the Multiphysics Object-Oriented Simulation Environment. The model provides a blind prediction of the specimen temperature evolution during transient tests given a desired power signal. Initially, our model accurately predicts the transient motion of the control rods to achieve the desired reactor power profile. Subsequently, it predicts the specimen temperature based on the power deposited within the specimen. The simulation results show strong agreement with the measured reactor power and control rod positions; however, the specimen temperature is slightly overpredicted, primarily because of assumptions about surface emissivities. When considering a more accurate set of specimen emissivities, the predicted temperature aligns exceptionally well with the measured values according to post-analysis results. The simulation results will support the design and analysis of the National Aeronautics and Space Administration sponsored Sirius series of experiments for nuclear thermal propulsion applications, and the model can be utilized to assist in the design and optimization of new experiments to be conducted at the TREAT Facility.