Deep Fission Dropped Its Criticality Timeline. The IPO Is Still Happening.
Deep Fission Dropped Its Criticality Timeline. The IPO Is Still Happening.
Deep Fission is asking public investors for up to $1.66 billion. It cannot yet say when — or whether — its reactor will ever work.
The Berkeley, California-based startup filed its IPO prospectus on May 20th, 2026, seeking to raise $157 million by selling 6 million shares at $24 to $26 each. The filing arrived eight months after Deep Fission completed a reverse merger with a Delaware shell company called Surfside Acquisition — a maneuver it marketed as "going public" even though the stock never traded on any exchange. In that failed SPAC transaction, investors paid $3 per share. The new IPO is priced at $24 to $26.
Buried in the December 2025 version of the same prospectus, the company told investors it expected to achieve criticality — the moment a nuclear reactor first sustains a fission chain reaction — by July 2026. In the May filing, that timeline is gone. The company will not say when it expects to reach criticality. It will not say when it expects to begin construction.
What Deep Fission can show investors is a test well being drilled in Parsons, Kansas. As of March 2026, that well had reached roughly 6,000 feet below the surface. Its diameter: approximately eight inches.
Deep Fission commercial reactor concept requires boreholes 30 to 50 inches in diameter, drilled to a depth of roughly a mile. The company has not drilled a borehole at anything approaching commercial scale.
The company raised $4 million in 2024 and $30 million through its September 2025 SPAC transaction — approximately $34 million in total external funding before its IPO roadshow. Its accumulated deficit stood at $88.1 million as of March 2026, up from $56.2 million four months earlier. Cash reserves fell by $6.4 million in roughly the prior six weeks. Both the December and May filings carry a going-concern warning: if the IPO fails, the company may run out of money within twelve months.
Deep Fission did receive an $80 million equity investment ahead of the IPO, including $20 million from Blue Owl, a data center developer, which signed a non-binding memorandum of understanding to discuss building power plants powered by Deep Fission reactors. The MOU is not a power purchase agreement. It is not a commitment. It is a conversation.
The company was selected for the Department of Energy Reactor Pilot Program in August 2025, alongside nine other advanced reactor designs. The program publicly stated goal is for at least three designs to achieve criticality by July 4th, 2026 — a deadline that appears in World Nuclear News coverage of the selection round. Deep Fission May prospectus does not reference it as a commitment or a target.
The company independent technical credibility rests partly on a thermal-hydraulics verification project being conducted by Idaho National Laboratory using a code called RELAP5-3D, which models how heat moves through the reactor system under normal and off-normal conditions. The project is underway. Its findings are not yet public.
Deep Fission was founded in 2023 by father-daughter team Elizabeth and Richard Muller, who previously co-founded a company called Deep Isolation in 2016, which proposed disposing of spent nuclear fuel by dropping it into deep boreholes. Deep Isolation raised money and signed partnerships, but did not achieve commercial deployment. Deep Fission is proposing to put the reactor in the same kind of hole.
The only comparable nuclear IPO in recent memory is X-energy, which raised $1.02 billion on April 24th, 2026 — the largest nuclear public offering on record — and saw its shares close 27 percent higher on their first day of trading. X-energy has received $1.4 billion in prior private funding, has partnerships with Amazon, Dow, and Centrica, holds an 11-gigawatt order pipeline, and received NRC licensing approval for its TRISO particle fuel manufacturing facility in February 2026. X-energy has also not yet begun construction on any of its reactor facilities.
Deep Fission is seeking a valuation that approaches X-energy while having raised roughly forty times less private capital, having achieved no regulatory milestones, and having produced no revenue.
When asked for comment on the timeline omission and the scale gap between its test well and its commercial concept, Deep Fission directed TechCrunch to its public filings. Those filings are the story.
The IPO roadshow is ongoing. The criticality timeline is not in them.