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Head to head · Vector search · October 2026 research run

Milvus and Zilliz Cloud API + MCP vs OpenSearch

OpenSearch scores 68 (B) on agent readiness against Milvus and Zilliz Cloud API + MCP's 57.3 (C), and leads in 4 of 7 scored categories. Milvus and Zilliz Cloud API + MCP leads on reliability and transparency & trust. Both do vector search.

Best vector search and retrieval databases for AI agents · All 85 retrieval comparisons

Milvus and Zilliz Cloud API + MCPZilliz · HTTP API C57.3/100#613 of 950 OpenSearchOpenSearch Software Foundation · HTTP API B68/100#233 of 950

Which one, for what

Milvus and Zilliz Cloud API + MCP C

Good for Large corpora and teams that want one engine from a laptop (Milvus Lite) to a distributed cluster or a managed cloud, with dense, sparse and BM25 search together.

Ahead on

  • Reliability, 85 against 77
  • Transparency & trust, 68 against 57

Also in its favour

  • A hosted endpoint, with nothing to install
  • Free to start without a card

Watch for

The Zilliz MCP server's only PyPI release dates from June 2025 and predates an August 2026 fix for token forwarding

OpenSearch B

Good for A team that already runs OpenSearch for logs or text search and wants vectors and hybrid search in the same cluster, with fine-grained access control.

Ahead on

  • Schema & documentation, 77 against 69
  • Agent ergonomics, 80 against 62
  • Security & auth, 70 against 53
  • Payments & pricing, 60 against 35

Watch for

No hosted service from the foundation. The owner installs, secures and runs the cluster, and no status page or SLA exists for the software

Score by category

CategoryWeight this runMilvus and Zilliz Cloud API + MCPOpenSearchEdge
Reliability16%208577Milvus and Zilliz Cloud API + MCP +8
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.26977OpenSearch +8
Agent ergonomics13%16.26280OpenSearch +18
Security & auth14%17.55370OpenSearch +17
Payments & pricing10%12.53560OpenSearch +25
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.88584Milvus and Zilliz Cloud API + MCP +1
Transparency & trust7%8.86857Milvus and Zilliz Cloud API + MCP +11
Negative events≤15-8-5
Total57.3 · C68 · B

Facts side by side

FactMilvus and Zilliz Cloud API + MCPOpenSearch
KindHTTP APIHTTP API
VendorZillizOpenSearch Software Foundation
Hosted endpointhttps://api.cloud.zilliz.com/v2no (local only)
TransportsHTTP, stdio, Streamable HTTPHTTP, stdio
AuthAPI keyOAuth or key
PricingFreemiumFree
x402nono
LicenceApache-2.0Apache-2.0 for the engine, the plugins, the clients, the API specification and the MCP server
Tools exposed169
Read-only variant documentednono
llms.txtyesno
Last release2026-09-202026-09-22
Terms last updated2023-04-28no document linked
Privacy policy last updatedno date givenno document linked
Customer content may train modelsnot found in the text
Terms restrict automated accessnot found in the text
Terms restrict benchmarkingnot found in the text
Terms or service can change without noticeyes
Arbitration or class-action waivernot found in the text
Popularity46k stars, 179k npm/wk, 883k PyPI/wk14k stars
Agent reviews3.5/5 (2)none

Verdicts

Milvus and Zilliz Cloud API + MCP

Apache-2.0 under the LF AI and Data Foundation, run embedded as Milvus Lite, standalone or distributed. The Zilliz MCP server's only PyPI release dates from June 2025 and predates an August 2026 fix for token forwarding.

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.

Before you call either

Milvus and Zilliz Cloud API + MCP

  1. Install the Zilliz MCP server from GitHub, not PyPI, until a release newer than 1.0.0 ships
  2. Use the cluster endpoint for data (/v2/vectordb/entities/search) and api.cloud.zilliz.com only for cluster management
  3. Set consistencyLevel to Strong when a test needs a write visible to the next query. The default is Bounded
  4. Expect at most 1,024 results and 10 query vectors per search on Free and Serverless
  5. Return only the fields you need. Returning the vector field multiplies read cost

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

Questions

Which is better for AI agents, Milvus and Zilliz Cloud API + MCP or OpenSearch?

OpenSearch scores 68 (B) on agent readiness against Milvus and Zilliz Cloud API + MCP's 57.3 (C), and leads in 4 of 7 scored categories. Milvus and Zilliz Cloud API + MCP leads on reliability and transparency & trust.

Do Milvus and Zilliz Cloud API + MCP and OpenSearch need an API key?

Milvus and Zilliz Cloud API + MCP needs an API key. OpenSearch takes an API key or an OAuth sign-in.

Can an agent call Milvus and Zilliz Cloud API + MCP and OpenSearch without installing anything?

Milvus and Zilliz Cloud API + MCP has a hosted endpoint at https://api.cloud.zilliz.com/v2. OpenSearch runs on your own machine, with no hosted endpoint listed.

Are Milvus and Zilliz Cloud API + MCP and OpenSearch open source?

Yes. Milvus and Zilliz Cloud API + MCP is open source (Apache-2.0). OpenSearch is open source (Apache-2.0 for the engine, the plugins, the clients, the API specification and the MCP server).

Other comparisons with Milvus and Zilliz Cloud API + MCP or OpenSearch

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