Google Research has open-sourced MilleMiglia, a C++ instance generator that creates realistic benchmarks for optimizing one of the supply chain's most critical but understudied segments: middle-mile logistics. The tool fills a significant gap in operational research by providing the first public, standardized dataset for middle-mile delivery problems—a challenge that logistics companies have long kept proprietary due to competitive sensitivity, even as the middle-mile represents a substantial portion of overall supply chain costs. Unlike first and last-mile logistics, which focus on moving goods to and from distribution centers, the middle-mile functions as a complex relay race where shipments pass through multiple regional hubs over several days. At each distribution center, goods must arrive within specific time windows to catch scheduled outgoing vehicles; missing these connections causes significant delays. The tool captures these unique constraints to generate privacy-preserving data applicable to e-commerce, retail, pharmaceuticals, and automotive supply chains. Google has published MilleMiglia's source code and documentation on GitHub, positioning it as a foundational resource for researchers seeking to optimize continental-scale logistics networks. The release addresses a persistent challenge in operations research where the lack of public data has hindered academic progress in one of the most expensive and complex segments of modern supply chains.