The Massive Legal Embedding Benchmark (MLEB)
Authors: name: Umar Butler, name: Abdur-Rahman Butler, name: Adrian Lucas Malec
Organization: Isaacus

We present the Massive Legal Embedding Benchmark (MLEB), the largest, most
diverse, and most comprehensive open-source benchmark for legal information
retrieval to date. MLEB consists of ten expert-annotated datasets spanning
multiple jurisdictions (the US, UK, EU, Australia, Ireland, and Singapore),
document types (cases, legislation, regulatory guidance, contracts, and
literature), and task types (search, zero-shot classification, and question
answering). Seven of the datasets in MLEB were newly constructed in order to
fill domain and jurisdictional gaps in the open-source legal information
retrieval landscape. We document our methodology in building MLEB and creating
the new constituent datasets, and release our code, results, and data openly to
assist with reproducible evaluations.