Marathon Fusion develops fuel cycle technologies to support fusion energy production. The company focuses on three areas: transmutation using neutrons to produce radioisotopes and gold as additional value sources beyond power generation; advanced pumping technologies for fuel processing to enhance tritium burn efficiency and speed; and isotope separation to supply critical materials for fusion and industrial applications. Founded in 2023 by Adam Rutkowski, formerly a propulsion engineer at SpaceX and PhD candidate in plasma physics at Princeton University, and Kyle Schiller, previously a fellow in science policy at Schmidt Futures. Marathon Fusion has received awards from the US Department of Energy, support from the Breakthrough Energy Fellows program, and investment from 1517 Fund and Strong Atomics. The company closed a seed funding round, as reported by PR Newswire. It has garnered press coverage in The New York Times, The Atlantic, Financial Times, The Telegraph, and The Times, highlighting efforts such as using nuclear fusion to transmute mercury into gold. Marathon Fusion targets the fusion energy sector while addressing needs in radioisotope production and materials supply.