Deep Fission, the Berkeley-based nuclear startup building underground reactors to power AI data centers, has filed an S-1 registration statement for a Nasdaq IPO targeting up to $156 million. The company plans to sell 6 million shares at a price range of $24 to $26, which would value the company at roughly $1.66 billion.

Less than a year ago, Deep Fission went public through a SPAC merger that raised $30 million at $3 per share. Now it’s asking investors to pay eight times that price for a spot on a far more prominent exchange.

From OTCQB to Nasdaq: a very different pitch

Deep Fission completed a reverse merger with Surfside Acquisition Inc. in September 2025. That deal landed the company on the OTCQB marketplace. The new filing, submitted on May 20, 2026, under the ticker FISN, targets Nasdaq, which opens the door to institutional investors who won’t touch OTCQB-listed companies.

Between the SPAC and the IPO attempt, Deep Fission closed an $80 million financing round in February 2026.

The technology: burying nuclear reactors on purpose

Deep Fission’s core product is the Gravity Nuclear Reactor, a small modular reactor designed to be placed approximately one mile underground in deep boreholes. Underground placement reduces the need for large containment structures by using surrounding rock for natural containment and radiation shielding.

The company was founded in 2023 by physicist Richard A. Muller and his daughter Elizabeth “Liz” Muller. The pair previously co-founded Deep Isolation, which focused on nuclear waste disposal using borehole technology, and Berkeley Earth, a climate data initiative. Backing comes from 8VC, the venture firm led by Joe Lonsdale, a co-founder of Palantir.

Deep Fission is targeting pilot criticality by mid-2026 under a U.S. Department of Energy initiative.

Why this matters beyond nuclear energy

The valuation jump from a $3 per share SPAC to a $24–$26 IPO range implies the company believes its value has increased roughly eightfold in under a year. The $80 million February financing round may have been priced at a level that supports this range, but without knowing those terms, investors are left doing math with missing variables.

Investors considering FISN should watch two things closely: the SEC’s response to the S-1 filing, and whether institutional allocations materialize at the proposed price range.