A little-known nuclear startup, Deep Fission Inc. based in Berkeley, California, has filed for an initial public offering with a $1.66 billion implied valuation. The company plans to raise up to $156 million by selling 6 million shares priced between $24 and $26 each.
Deep Fission filed its S-1 registration statement on May 20, 2026, and will trade under the ticker FISN on the Nasdaq. Underwriters include William Blair, Stifel, and Canaccord Genuity.
The company's Gravity Nuclear Reactor is a small modular reactor designed to be built underground in deep boreholes. This approach, Deep Fission claims, can cut construction costs by 70 to 80 percent compared to conventional reactors, using the earth itself as containment.
In February 2026, Deep Fission closed an $80 million financing round and secured a pilot reactor agreement with the Department of Energy in Kansas, targeting commercial deployment by 2027-2028. Its non-binding pipeline currently totals 15 GWe.
The startup has also partnered with Endeavour Energy to supply up to 2 GW of power for AI data centers, positioning itself to capture surging demand from the tech sector.
CEO Elizabeth Muller previously founded Deep Isolation, a company specializing in nuclear waste disposal via deep boreholes.
For investors, this is a pre-revenue bet on execution. The 2027-2028 timeline means revenue is at least a year away. Whether Deep Fission can convert its pipeline into contracts will determine if the $1.66 billion valuation is prescient or premature.