Solar Energetic Particle (SEP) events remain one of the most consequential and least predictable elements of space weather, driving radiation hazards for crewed missions, polar aviation, spacecraft electronics, and dependent ground infrastructure. As human and commercial activity in cislunar space expands, operational SEP forecasting has become a mission-critical need. Yet three long-standing problems continue to limit progress: (i) identifying SEP seed populations, (ii) characterizing acceleration across varied solar and interplanetary conditions, and (iii) modeling transport through a structured heliospheric magnetic field. Predicting the arrival and spectrum of the highest-energy SEPs, which pose the greatest risk, remains particularly challenging.

This session solicits contributions that identify specific gaps in SEP forecasting and advance mitigation strategies. We welcome work on new and planned observing infrastructure, near-real-time and extended-baseline data sets, and forecasting frameworks spanning physics-based, statistical, machine-learning, and hybrid approaches, with emphasis on translating fundamental SEP physics into operational capability.