Meet LEANN: An Open-Source Vector Index that Shrinks a 60M-Chunk RAG Index from 201 GB to 6 GB
UC Berkeley’s Sky Computing Lab built LEANN , an open-source vector index that stores almost no embeddings. The LEANN vector index recomputes embeddings at query time instead of saving them to disk. The repo benchmark shows a 60 million chunk Wikipedia index dropping from 201 GB to 6 GB. The research paper won the Best Research Paper award at MLSys 2026 . So, it brings semantic search and RAG over personal data, on a laptop. TL;DR Size: 6 GB for 60M chunks ( repo ); 4 GB in the paper’s 76 GB Wikipedia setup. Default embedder: Contriever (110M params). It is an index, not an LLM, so no context length applies. Runs on: laptops and workstations. The paper tested an RTX 4090 box with 32 GB RAM and an M1 Ultra Mac. A CPU-only Linux install exists, with no published CPU latency. Performance: matches HNSW downstream accuracy at 90% recall, using under 5% of raw-data storage. Best: 25.5% NQ accuracy, identical to HNSW, using 4 GB instead of 188 GB. ...
