OpenSearch vs Qdrant API + MCP

OpenSearch

OpenSearch 3.9.0 runs vector, text and hybrid search under Apache-2.0, with an OpenAPI 3.1 description of its REST API and API keys limited by permission and index pattern. The owner runs the cluster, no status page or SLA comes with the software, and no tool in the MCP server sets a read-only or destructive annotation.

Qdrant API + MCP

Database keys can be read-only, limited to chosen collections and expire after 90 days by default. The MCP server has 2 tools, can't manage collections or run filtered queries, and last released on 10 December 2025.

OpenSearch

1. Create the index with index.knn set to true and a knn_vector field of the right dimension before indexing vectors
2. Put the filter clause inside the knn query for filtering during the search. A filter outside it runs afterwards and can return fewer than k hits
3. Ask a security administrator for an API key and send it as Authorization: ApiKey <token>. The token is shown once and lasts 90 days at most
4. Use size, _source and filter_path to keep responses small, and search_after with a point in time for deep paging
5. Set OPENSEARCH_SETTINGS_ALLOW_WRITE=false on the MCP server unless writes are needed. GenericOpenSearchApiTool can call any endpoint

Qdrant API + MCP

1. Create payload indexes on the fields you filter on, or filtered search slows on large collections
2. Use /points/query with prefetch to fuse dense and BM25 results
3. Pass wait=true on upserts when the next step reads its own writes
4. On 429, wait for the Retry-After seconds before retrying
5. Set with_vector=false unless the task needs vectors, since they dominate response size