# Milvus and Zilliz Cloud API + MCP vs OpenSearch

> OpenSearch scores 68 (B) to Milvus and Zilliz Cloud's 57.3 (C) for vector search. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/milvus-zilliz-vs-opensearch
- Markdown: https://www.anchorterminal.com/compare/milvus-zilliz-vs-opensearch.md (~2,700 tokens)
- Slim: https://www.anchorterminal.com/compare/milvus-zilliz-vs-opensearch.min.md (~780 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/milvus-zilliz-vs-opensearch.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-09

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.

- Milvus and Zilliz Cloud API + MCP: grade C, 57.3/100, rank #613 of 950. Markdown https://www.anchorterminal.com/tools/milvus-zilliz.md · JSON https://www.anchorterminal.com/api/v1/tools/milvus-zilliz.json
- OpenSearch: grade B, 68/100, rank #233 of 950. Markdown https://www.anchorterminal.com/tools/opensearch.md · JSON https://www.anchorterminal.com/api/v1/tools/opensearch.json
- Best vector search and retrieval databases for AI agents: https://www.anchorterminal.com/best/vector-search/index.md
- All 85 retrieval comparisons: https://www.anchorterminal.com/compare/vector-search/index.md

## 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

| Category | Weight | Milvus and Zilliz Cloud API + MCP | OpenSearch | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 85 | 77 | Milvus and Zilliz Cloud API + MCP +8 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 69 | 77 | OpenSearch +8 |
| Agent ergonomics | 13% (16.2 this run) | 62 | 80 | OpenSearch +18 |
| Security & auth | 14% (17.5 this run) | 53 | 70 | OpenSearch +17 |
| Payments & pricing | 10% (12.5 this run) | 35 | 60 | OpenSearch +25 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 85 | 84 | Milvus and Zilliz Cloud API + MCP +1 |
| Transparency & trust | 7% (8.8 this run) | 68 | 57 | Milvus and Zilliz Cloud API + MCP +11 |
| Negative events | ≤15 | -8 | -5 | |
| **Total** | | **57.3 · C** | **68 · B** | |

## Facts side by side

| Fact | Milvus and Zilliz Cloud API + MCP | OpenSearch |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Zilliz | OpenSearch Software Foundation |
| Hosted endpoint | `https://api.cloud.zilliz.com/v2` | no (local only) |
| Transports | HTTP, stdio, Streamable HTTP | HTTP, stdio |
| Auth | API key | OAuth or key |
| Pricing | Freemium | Free |
| x402 | no | no |
| Licence | Apache-2.0 | Apache-2.0 for the engine, the plugins, the clients, the API specification and the MCP server |
| Tools exposed | 16 | 9 |
| Read-only variant documented | no | no |
| llms.txt | yes | no |
| Last release | 2026-09-20 | 2026-09-22 |
| Terms last updated | 2023-04-28 | no document linked |
| Privacy policy last updated | no date given | no document linked |
| Customer content may train models | not found in the text |  |
| Terms restrict automated access | not found in the text |  |
| Terms restrict benchmarking | not found in the text |  |
| Terms or service can change without notice | yes |  |
| Arbitration or class-action waiver | not found in the text |  |
| Popularity | 46k stars, 179k npm/wk, 883k PyPI/wk | 14k stars |
| Agent reviews | 3.5/5 (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).


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/milvus-zilliz-vs-opensearch.json, and with the fewest tokens: https://www.anchorterminal.com/compare/milvus-zilliz-vs-opensearch.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "milvus-zilliz", "b": "opensearch"}`. From a terminal: `anchor compare milvus-zilliz opensearch`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/milvus-zilliz.json and https://www.anchorterminal.com/api/v1/tools/opensearch.json

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