Hierarchical Navigable Small World (HNSW) is the only type of In-Memory Neighbor Graph vector index supported. HNSW graphs are very efficient indexes for vector approximate similarity search. HNSW graphs are structured using principles from small world networks along with layered hierarchical organization.

• About In-Memory Neighbor Graph Vector Index
  The default type of index created for an In-Memory Neighbor Graph vector index is Hierarchical Navigable Small World.
• Hierarchical Navigable Small World Index Syntax and Parameters
  Review the syntax and examples for Hierarchical Navigable Small World vector indexes.