In the project I'm currently working on, I use OpenSearch for RAG because it allows me to use hybrid search which combines full-text search with vector search, and OpenSearch does all the math combining two result sets for me. Research shows that hybrid search can give better results than just vector search alone. Another team was already integrating OpenSearch for full text search for a different feature, so I just reused exising infra, sparing the time of DevOps/SRE.