How do vector databases handle multi-tenancy?

Multi-tenancy isolates data between users or customers sharing the same cluster. Pinecone uses namespaces within an index, Weaviate has first-class multi-tenancy with per-tenant shards that can be hot or cold, Qdrant uses collections or payload-based tenant filtering, and Milvus supports databases and collections as isolation units. Strong multi-tenancy requires per-tenant quotas, isolated indexes for performance, and security guarantees that one tenant cannot access another's data. Weaviate's dedicated multi-tenancy feature is the most feature-complete for SaaS workloads.