The vast uncertainty in the contribution of the Antarctic Ice Sheet (AIS) to sea level rise is dominated by poorly understood and highly nonlinear processes at the interface between the ice sheet and adjacent ocean and atmosphere.  At the same time, few of these interactions are represented in any ice sheet models or Earth system models.  The Energy Exascale Earth System Model (E3SM) is in a leading position to address these challenges, but key linkages and ice-sheet processes remain unresolved in E3SM.  The FAnSSIE will establish a full, integrated representation of Antarctica in the coupled Earth system within E3SM and create a workflow for probabilistically quantifying AIS impacts on sea level change at decadal and centennial scales.  Model development within E3SM will introduce key missing processes: migration of the ocean model into newly deglaciated regions as AIS retreats, and the retention of meltwater within the surface snowpack and the potential “hydrofracture” of that snow through the ice leading to ice-shelf disintegration.  Model development within the MALI ice-sheet model within E3SM will introduce a representation of ice fracture mechanics that is coupled to ice flow dynamics using advanced computational methods including unstructured mesh adaptivity to follow rifts as they form.  Additionally, improvements in dynamic load balancing, hardware portability, and software modernization will ensure the enhanced MALI and E3SM models can take full advantage of DOE Exascale computing investments.  Finally, these E3SM and MALI developments will be applied to a series of interconnected simulation campaigns quantifying the uncertainty in the AIS contribution to future sea level rise.