According to co-founder Kyle Schiller:
Marathon Fusion builds the fuel cycle for fusion energy. Right now, we’re developing the super-permeable metal foil pump, a component capable of enabling the Direct Internal Recycling loop for fusion power plants. This advanced fuel cycle architecture allows for greatly reduced tritium inventories, with beneficial effects to cost, safety, deployability, and regulatory barriers. We have an LOI signed with Commonwealth Fusion Systems to procure the pump, and existing investments from a great set of angels including Malcom Handley, the former tech-to-market advisor on fusion for ARPA-E.
See Metal foil pumps for direct internal recycling in fusion reactors