Oklo Inc. just did something that most of the nuclear industry considered ambitious, if not borderline reckless, on the timeline front. The company’s Groves Isotope Test Reactor has achieved first criticality, meaning a self-sustaining nuclear chain reaction at low power. For a privately financed reactor that broke ground less than a year ago, that’s not just fast. It’s a signal to every energy investor paying attention.
The NYSE-listed company (ticker: OKLO) had been running a public campaign called #CountdownToCriticality in recent weeks, tracking startup tests including core loading and control rod checks. Those tests began in early August 2026, shortly after the US Department of Energy granted startup authorization on July 23, 2026.
From dirt to fission in under twelve months
Oklo’s approach with the Groves reactor looks nothing like the traditional nuclear playbook. The facility, a pool-type, water-cooled reactor located in Caldwell County, Texas, was designed from the start to move quickly. It uses low-enriched uranium fuel sourced commercially, sidestepping the procurement bottlenecks that have historically strangled timelines for more exotic fuel types.
The DOE’s approval came under its Reactor Pilot Program, a framework specifically built to get advanced reactors deployed outside the traditional national laboratory system.
Jacob DeWitte, Oklo’s CEO, has pointed to the speed from groundbreaking to criticality as a potential model for commercial nuclear timelines going forward.
What the Groves reactor actually does
This isn’t a power plant. The Groves reactor is designed primarily to support isotope production and to generate operational data for Oklo’s future, larger-scale facilities.
Medical isotopes are essential for cancer diagnostics and treatment. Research isotopes support everything from materials science to national security applications. The US has historically relied heavily on aging reactors and foreign supply chains for these materials, creating a vulnerability that policymakers have been trying to address for years.
The operational data piece is arguably just as important. Every hour the Groves reactor runs generates insights that feed directly into the design and licensing of Oklo’s planned commercial reactors.
What this means for investors
The risk side of the ledger is straightforward. This is still a low-power test reactor, not a commercial facility. Scaling from a successful test to a fleet of revenue-generating reactors involves regulatory, engineering, and financing hurdles that have tripped up plenty of nuclear startups before. The Nuclear Regulatory Commission pathway for commercial-scale reactors is a different beast entirely from the DOE’s Reactor Pilot Program.