Expanse is a clean-room, pure-Rust implementation of Judy arrays — sparse, dynamic associative structures built as 256-ary digital tries partitioned by key range (expanse) rather than by population — modernized for current 64-bit and 32-bit embedded microarchitectures. It ships libexpanse, a high-performance drop-in C ABI replacement for libjudy, plus Go, Node.js, .NET and Python bindings.Dual-licensed MIT OR Apache-2.0. This record lists Apache-2.0 because Zenodo accepts a single licence identifier; the MIT option applies equally (see LICENSE-MIT in the archived source).