15 MWt pool-type, water-cooled, nonpressurised isotope test reactor on a greenfield private-land site at Oklo's Groves facility in Lockhart, Texas, south of Austin. It reached first criticality at 9:19 p.m. EDT on August 5, 2026, in under a year from a greenfield start. It was the fifth DOE-authorised reactor to reach criticality under the Reactor Pilot Program and the first on private land. It is a test platform for future production-scale isotope reactors serving medicine, industry, research, space and national security, and is meant to inform Oklo's Powerhouse and fuel-cycle facilities. DOE startup authorisation was granted on July 23, 2026. Capacity is given as thermal output (15 MWt); no electrical capacity is recorded.