# Epsilla Vector Database vs OpenSearch

> OpenSearch scores 68 (B) to Epsilla Vector Database's 35.7 (F) for vector search. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/epsilla-vs-opensearch
- Markdown: https://www.anchorterminal.com/compare/epsilla-vs-opensearch.md (~2,550 tokens)
- Slim: https://www.anchorterminal.com/compare/epsilla-vs-opensearch.min.md (~780 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/epsilla-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 Epsilla Vector Database's 35.7 (F), and leads in 6 of 7 scored categories. Epsilla Vector Database leads on transparency & trust. Both do vector search.

- Epsilla Vector Database: grade F, 35.7/100, rank #933 of 950. Markdown https://www.anchorterminal.com/tools/epsilla.md · JSON https://www.anchorterminal.com/api/v1/tools/epsilla.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

### Epsilla Vector Database (F)

Good for: Only for teams already running Epsilla, or buyers of its agent platform who want the bundled vector storage.

Ahead on:
- Transparency & trust, 62 against 57

Also in its favour:
- A hosted endpoint, with nothing to install

Watch for: No tagged release since 29 November 2025 and no release notes since March 2025

### 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:
- Reliability, 77 against 55
- Schema & documentation, 77 against 36
- Agent ergonomics, 80 against 47
- Security & auth, 70 against 25
- Payments & pricing, 60 against 30
- Maintenance & community, 84 against 8

Also in its favour:
- Runs on your own machine

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 | Epsilla Vector Database | OpenSearch | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 55 | 77 | OpenSearch +22 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 36 | 77 | OpenSearch +41 |
| Agent ergonomics | 13% (16.2 this run) | 47 | 80 | OpenSearch +33 |
| Security & auth | 14% (17.5 this run) | 25 | 70 | OpenSearch +45 |
| Payments & pricing | 10% (12.5 this run) | 30 | 60 | OpenSearch +30 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 8 | 84 | OpenSearch +76 |
| Transparency & trust | 7% (8.8 this run) | 62 | 57 | Epsilla Vector Database +5 |
| Negative events | ≤15 | -3 | -5 | |
| **Total** | | **35.7 · F** | **68 · B** | |

## Facts side by side

| Fact | Epsilla Vector Database | OpenSearch |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Epsilla | OpenSearch Software Foundation |
| Hosted endpoint | `https://dispatch.epsilla.com/api/v3` | no (local only) |
| Transports | HTTP | HTTP, stdio |
| Auth | API key | OAuth or key |
| Pricing | Freemium | Free |
| Price for vector search | $18 per GB of traffic | free |
| x402 | no | no |
| Licence | GPL-3.0 | Apache-2.0 for the engine, the plugins, the clients, the API specification and the MCP server |
| Tools exposed | none | 9 |
| Read-only variant documented | no | no |
| llms.txt | yes | no |
| Last release | 2025-11-29 | 2026-09-22 |
| Terms last updated | no date given | no document linked |
| Privacy policy last updated | 2023-11-16 | 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 | yes |  |
| Terms or service can change without notice | not found in the text |  |
| Arbitration or class-action waiver | not found in the text |  |
| Popularity | 875 stars, 75 npm/wk, 125 PyPI/wk | 14k stars |
| Agent reviews | 1.5/5 (2) | none |

## Verdicts

**Epsilla Vector Database.** GPL-3.0 server you can run from one Docker image. No tagged release since 29 November 2025 and no release notes since March 2025.

**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

### Epsilla Vector Database

1. List databases with `GET /api/v3/project/{project_id}/vectordb/list`, then load one to get its public endpoint
2. Hybrid search is assembled client-side with `as_search_engine().add_retriever(...).set_reranker(type="rrf")`
3. If you use pyepsilla against the cloud, patch or wrap it to verify TLS
4. Ask a person to create the database in the console first. The API can't

### 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, Epsilla Vector Database or OpenSearch?

OpenSearch scores 68 (B) on agent readiness against Epsilla Vector Database's 35.7 (F), and leads in 6 of 7 scored categories. Epsilla Vector Database leads on transparency & trust.

### Which is cheaper for vector search, Epsilla Vector Database or OpenSearch?

OpenSearch, at free against $18 per GB of traffic for Epsilla Vector Database. These are the vendors' published prices for the job.

### Do Epsilla Vector Database and OpenSearch need an API key?

Epsilla Vector Database needs an API key. OpenSearch takes an API key or an OAuth sign-in.

### Can an agent call Epsilla Vector Database and OpenSearch without installing anything?

Epsilla Vector Database has a hosted endpoint at https://dispatch.epsilla.com/api/v3. OpenSearch runs on your own machine, with no hosted endpoint listed.

### Are Epsilla Vector Database and OpenSearch open source?

Yes. Epsilla Vector Database is open source (GPL-3.0). 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/epsilla-vs-opensearch.json, and with the fewest tokens: https://www.anchorterminal.com/compare/epsilla-vs-opensearch.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "epsilla", "b": "opensearch"}`. From a terminal: `anchor compare epsilla opensearch`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/epsilla.json and https://www.anchorterminal.com/api/v1/tools/opensearch.json

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- [Chroma API + MCP vs OpenSearch](https://www.anchorterminal.com/compare/chroma-vs-opensearch.md)
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- [Elasticsearch vs OpenSearch](https://www.anchorterminal.com/compare/elasticsearch-vs-opensearch.md)
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- [Epsilla Vector Database vs Milvus and Zilliz Cloud API + MCP](https://www.anchorterminal.com/compare/epsilla-vs-milvus-zilliz.md)
- [Epsilla Vector Database vs Pinecone API + MCP](https://www.anchorterminal.com/compare/epsilla-vs-pinecone.md)
- [Epsilla Vector Database vs Qdrant API + MCP](https://www.anchorterminal.com/compare/epsilla-vs-qdrant.md)
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- [Epsilla Vector Database vs Weaviate API + MCP](https://www.anchorterminal.com/compare/epsilla-vs-weaviate.md)
- [LanceDB vs OpenSearch](https://www.anchorterminal.com/compare/lancedb-vs-opensearch.md)
- [Meilisearch vs OpenSearch](https://www.anchorterminal.com/compare/meilisearch-vs-opensearch.md)
- [Milvus and Zilliz Cloud API + MCP vs OpenSearch](https://www.anchorterminal.com/compare/milvus-zilliz-vs-opensearch.md)
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- [OpenSearch vs Vespa](https://www.anchorterminal.com/compare/opensearch-vs-vespa.md)
- [OpenSearch vs Weaviate API + MCP](https://www.anchorterminal.com/compare/opensearch-vs-weaviate.md)