A nuclear startup you’ve probably never heard of just filed to go public with a $1.66 billion implied valuation. Deep Fission Inc., based in Berkeley, California, wants to raise up to $156 million through a US initial public offering, selling 6 million shares priced between $24 and $26 each.
The company filed its S-1 registration statement on May 20, 2026, and plans to trade under the ticker FISN on the Nasdaq. William Blair, Stifel, and Canaccord Genuity are handling the underwriting. The capital will fund the development of what Deep Fission calls its Gravity Nuclear Reactor, a small modular reactor designed to be built underground in deep boreholes.
The pitch: nuclear reactors, but cheaper and underground
Deep Fission claims its underground borehole approach can cut construction costs by 70 to 80 percent compared to conventional reactor builds. Instead of building a massive above-ground facility with layers of concrete containment, Deep Fission wants to drill deep holes and let the earth itself serve as the containment structure.
In February 2026, Deep Fission closed an $80 million financing round. It has also locked in a pilot reactor agreement with the Department of Energy in Kansas. Commercial deployment is targeted for the 2027-2028 timeframe.
