Faiss

Faiss is Meta's open-source library for dense-vector similarity search and clustering, not a hosted vector database. Rechecked 2026-08-18: github.com/facebookresearch/faiss had 40,752 stars, license MIT, homepage faiss.ai. faiss.ai and the README still describe algorithms that can search vectors that do not fit in RAM, plus evaluation helpers. Drop leftover "social media giant / powerful ally" marketing.

Compare pgvector if you wanted vectors inside PostgreSQL, Qdrant if you wanted a dedicated OSS engine plus Cloud, and Pinecone if you wanted a managed dollar table.

Key Features

• Library, not a cloud: You link C++ / Python (and related bindings) in your process. There is no Faiss SaaS seat on GitHub or faiss.ai.
• ANN algorithms: IVF, HNSW, PQ and related indexes, CPU and GPU paths. Treat the live README / faiss.ai as the algorithm list, not a leftover brochure.
• Out-of-RAM search: First-party copy still says it can search vectors that do not all fit in RAM. That is a library capability, not a hosted SLA.
• Not pgvector: pgvector is a Postgres extension. It is not "based on Faiss."

Use Cases

• People who will embed Faiss in a research or serving binary.
• Teams comparing 40,752 stars against a SQL extension or a vector Cloud.
• People who need GPU ANN and will operate the machines themselves.

Limitation: We did not invent a Faiss Cloud dollar. If a host wraps Faiss, that host's bill is not Faiss.

Pricing

GitHub and faiss.ai on 2026-08-18.

If a leftover blog still sells Faiss as a hosted vector service, treat this table as the source.

Getting Started

1. Open github.com/facebookresearch/faiss or faiss.ai.
2. Recheck pgvector if you wanted SQL types instead of a library.
3. Recheck Qdrant if you wanted a server and a Cloud node.
4. Do not paste "social media giant" into a product page.

Frequently Asked Questions

Is it free?

Yes. MIT. You pay for the machines you run it on.

Is it a vector database?

No. It is a similarity-search library. Persistence, multi-tenant Cloud, and SQL are other products.

Same as pgvector?

No. pgvector adds vector types and indexes to Postgres. It is not a Faiss wrapper.

Alternatives

• pgvector: Postgres extension, PostgreSQL license, 22,651 stars.
• Qdrant: OSS vector engine plus Cloud Free / usage-based Standard.
• Pinecone: Managed vector DB with public dollar rows.
• Vespa: Search + ranking serving engine that also does vectors.

Tips

1. Quote 40,752 stars and MIT from the GitHub check.
2. Call it a library, not a hosted DB.
3. Recheck pgvector if someone still says that extension is Faiss.

Conclusion

Faiss is a MIT similarity-search library with 40,752 stars, not a hosted vector DB and not a leftover marketing ally. Start at github.com/facebookresearch/faiss or faiss.ai, then decide whether pgvector or Qdrant already covers the product shape you need.