Apollo Atomics has raised $26 million, including $5 million in debt, to build a demonstration reactor and advance planned commercial deployment in 2028. The company, founded by Assil Halimi and Drew Walker and part of Y Combinator’s Spring 2026 batch, is redesigning the steam generator rather than the reactor itself. Apollo says its compact, mass-manufactured component could make a reactor system about 40 times smaller than one using a conventional steam generator, support factory assembly and enable deployment in less than 24 months. Halimi projects electricity costs of 3 cents per kilowatt-hour and says the company aims to beat natural gas. Apollo is developing 10-megawatt, 50-megawatt and 300-megawatt electric systems and has already built a 40-kilowatt reactor at MIT. An earlier company financing announcement described a $31 million seed round; the newer financing disclosure describes $26 million, including debt.