This is a Sources Sought Notice (SSN) issued by the Alliance for Energy Innovation, LLC (Alliance). The purpose of this SSN is to conduct market research and gather information on the current capabilities of potential sources to provide expert development and technical advisory and training services for the Sienna software to advance NLR-prioritized platform features in support of NLR's energy systems research and technical assistance programs. Sienna is an open-source energy systems modeling platform developed and stewarded by the National Laboratory of the Rockies (NLR). Built primarily in Julia, Sienna provides a suite of tools for power systems simulation, capacity planning, power flow analysis, and results analytics, and serves as a core platform for NLR research, technical assistance, and applied analysis projects. Sienna is actively used in domestic and international engagements with government energy authorities, regulators, utilities, and system operators. NLR seeks subcontract support for targeted Sienna software development, technical advisory, and training services to advance platform capabilities in alignment with NLR's research and project objectives.