FAISS

Facebook AI Research Similarity Search. C++ library with Python bindings for efficient similarity search and clustering of dense vectors. Supports flat (exact), IVF (approximate), HNSW, PQ, and many other index types. CPU-only via PyPI (faiss-cpu); GPU support requires conda or building from source. Officially maintained by Meta/Facebook AI Research; PyPI wheel builds maintained by the community (faiss-wheels project). Import is always 'import faiss' regardless of which package is installed.