Deep Fission, Valar Atomics, and Radiant Industries are three nuclear-energy startups developing smaller alternatives to traditional nuclear plants. Deep Fission plans to install approximately 15-megawatt reactors deep underground, which could reduce construction and containment costs. However, its technology remains at an early stage and still requires significant testing, regulatory approval, and additional financing. Valar Atomics is developing high-temperature gas reactors for electricity and industrial heat. It appears to be the most technically advanced of the three because it has already achieved reactor criticality, but it remains a private company with a high valuation. Radiant Industries is developing Kaleidos, a portable one-megawatt microreactor designed to replace diesel generators at military bases and remote locations. Its smaller size and clearly defined market may make commercialization easier. Overall, Valar has made the strongest technical progress, Radiant may have the most practical early business model, and Deep Fission offers the greatest speculative investment opportunity because it is publicly traded, although it also carries the greatest risk.