head to head · open source
faiss vs LangWatch
faiss has 40,939 GitHub stars, 4,527 forks, 327 open issues and last shipped 2 days ago. LangWatch has 4,833 stars, 395 forks, 939 open issues and last shipped 2 days ago. faiss leads on adoption by 747% (40,939 vs 4,833 stars). faiss is written in C++ under MIT; LangWatch is written in TypeScript under Apache-2.0. faiss has attracted 11% as many forks as stars, LangWatch 8%. faiss was the more recently maintained of the two, and both are self-hostable with no licence fee.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| faiss | LangWatch | |
|---|---|---|
| GitHub stars | ★ 41K | ★ 4.8K |
| License | MIT | Apache-2.0 |
| Written in | C++ | TypeScript |
| Last push | 2026-09-19 | 2026-09-19 |
| Forks | ⑂ 4.5K | ⑂ 395 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick faiss if
- You weight community size — 41K stars and counting
- You want the MIT license terms
- Your stack matches C++
- You value the larger contributor base for long-term maintenance
pick LangWatch if
- You want the LangWatch feature set and don't need the biggest community
- You prefer the Apache-2.0 license terms
- Your stack matches TypeScript
- You evaluated both and LangWatch fits your workflow better
About faiss
Faiss is an MIT licensed C++ library for efficient similarity search and clustering of dense vectors, with complete Python and NumPy wrappers, developed primarily at Meta's Fundamental AI Research group, and it is intended for engineers and researchers who need nearest neighbour search over vector sets that range from small collections to sets that possibly do not fit in RAM.
read the full faiss overview →
About LangWatch
LangWatch is an open source TypeScript platform for LLM evaluations and AI agent testing, licensed under Apache 2.0. It lives in the machine learning infrastructure ecosystem for teams that build LLM powered agents and need to test, simulate, evaluate, and monitor agents before release and in production.
read the full LangWatch overview →
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Frequently asked questions
Is faiss or LangWatch more popular?
faiss has 40,939 GitHub stars and LangWatch has 4,833. faiss has the larger community by that measure.
Are faiss and LangWatch free?
Both are open source. faiss is licensed under MIT and LangWatch under Apache-2.0. Neither carries a licence fee.
What is the difference between faiss and LangWatch?
faiss is written in C++ and LangWatch in TypeScript. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, faiss or LangWatch?
Choose faiss if you want the larger community (40,939 stars) or its MIT licence terms. Choose LangWatch if its feature set, stack or Apache-2.0 licence fits better. Both are self-hostable.