California-based start-up Deep Fission, which is developing small modular reactors (SMRs) deployed in deep underground shafts, plans to raise $150m by offering 6m shares at a price range of $24-26. At the midpoint of the proposed range, Deep Fission would command a fully diluted market value of $1.7bn. The company plans to list on the Nasdaq under the symbol FISN.
William Blair, Stifel, and Canaccord Genuity are acting as joint lead book-running managers for the offering. Seaport Global Securities and Benchmark, a StoneX Company are acting as bookrunners for the offering.
Deep Fission, founded in 2023, is a developing a SMR based on pressurised water reactor technology. Its Gravity Nuclear Reactor is designed to be installed approximately one mile below the Earth’s surface, where subsurface conditions, including hydrostatic pressure from a water column and the surrounding geological formation, are intended to support containment, cooling, and shielding functions. The approach aims to reduce reliance on the large surface infrastructure associated with conventional nuclear plants, with the potential for lower capital costs, faster deployment, and improved security. Reactors may be deployed individually or in clustered configurations at a single site.
Deep Fission intends to use the net proceeds from this offering for general working capital and corporate purposes, including towards the engineering, research and development, licensing and construction of its first pilot nuclear reactor and related technologies.
It says its commercial strategy is focused on deploying Gravity Reactors in markets with rapidly growing electricity demand and increasing need for reliable, affordable baseload power. “Our initial commercial focus is on hyperscale data centres and other large power users, and over time may expand to include utilities, industrial operators, and government or defence installations”.
Deep Fission broke ground in December 2025 at the Great Plains Industrial Park in Parsons, Kansas, for its pilot project and plans to build a full-scale commercial plant there following the test reactor demonstration. In its filing with the US Securities and Exchange Commission, the company says that “in addition to the Kansas Site, we have entered into multiple non-binding LOIs (letters of intent) with potential development partners for candidate commercial sites in the United States. These LOIs relate to potential deployment opportunities in Kansas, Texas, and Utah as well as other locations in the United States and internationally”.
In August 2025, Deep Fission was one of 10 companies selected by the US Department of Energy to receive support under its Nuclear Reactor Pilot Program, which aims to see at least three designs achieve criticality by 4 July 2026. However, its new S-1 filing dropped its previous concrete target of achieving reactor criticality by July 2026, leaving the commercialisation date unspecified. The company has currently only commenced test-well drilling for data acquisition in Parsons, Kansas. It has not yet built, operated, or fully licensed a commercial reactor.
External auditors have included a stark warning that the company faces an accumulated deficit of $88.1m and could run out of cash within 12 months if the IPO is not executed. The external independent auditor for Deep Fission is DBBMcKennon, a Public Company Accounting Oversight Board-registered public accounting firm based in Newport Beach, California. They were appointed to audit the company’s financial records starting with the fiscal periods following Deep Fission’s commercial launch and initial public filings in 2025.
The specific details behind the auditor’s red flags are that the company reported net losses of $61m for the full year of 2025 and an additional $21.3m in the first quarter of 2026. As of 31 March, Deep Fission’s cumulative accumulated deficit rose to $88.1m – a sharp increase from the $56.2m reported just months earlier. The company’s cash reserves dropped by $6.4m (about 7%) over a recent 45-day period.
While it held $84.8m in cash as of 31 March, this will soon be taken up by massive operational overheads. The auditor highlights that Deep Fission has generated zero revenue to date. Capital is being consumed entirely by capital-intensive research and development (R&D), heavy general administrative overheads, test-well drilling in Parsons, Kansas, and the legal/regulatory process of listing.
