The Jezebel plutonium critical assembly, operated from 1954 to 1977, has been a benchmark for validating nuclear data, particularly for fast 239Pu fission, over the past 70 years. However, since its disassembly decades ago, there have been issues with Jezebel’s legacy, including incomplete documentation, limited opportunities for long-term system parameter observations, and a lack of means to test new advancements using the same assembly.Given these challenges, there is a pressing need for a new, enduring benchmark plutonium critical assembly capable of providing ongoing validation and data collection. Such an assembly would assist in nuclear data validation, reactor kinetics, dosimetry, and many other areas of nuclear research while helping maintain U.S. leadership in plutonium research.The concept of Lilith, a new enduring plutonium assembly currently under development, is introduced as a potential solution to address these needs. The design of Lilith focuses on a simple geometry, low uncertainties, and a planned lifetime of 100 years. Lilith will use a cylindrical design, which will allow for easier manufacturing and greater flexibility in adjusting its components over time.The enduring nature of the system will enable ongoing validation of nuclear data, analytical methods, dosimetry, reactor kinetics, and material properties across decades. This would also provide the opportunity for new measurements of reactor kinetics parameters using neutron noise methods, and long-term criticality studies, while tracking changes in the plutonium system over time. This work highlights the importance of such a system for future advancements in nuclear technology and the need to ensure the continued availability of such research capabilities.