Oklo’s Groves Isotope Test Reactor achieves first criticality, marking a milestone for private nuclear

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 c...