head to head · open source
faiss vs LangWatch
faiss has 41,256 GitHub stars, 4,586 forks, 327 open issues and last shipped 2 days ago. LangWatch has 5,011 stars, 425 forks, 939 open issues and last shipped yesterday. faiss leads on adoption by 723% (41,256 vs 5,011 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%. LangWatch 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 | ★ 5.0K |
| License | MIT | Apache-2.0 |
| Written in | C++ | TypeScript |
| Last push | 2026-11-03 | 2026-11-04 |
| Forks | ⑂ 4.6K | ⑂ 425 |
| 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 Faiss is a library for efficient similarity search and clustering of dense vectors. It contains algorithms that search in sets of vectors of any size, up to ones that possibly do not fit in RAM. It also contains supporting code for evaluation and parameter tuning. Faiss is written in C++ with complete wrappers for Python/numpy. Some of the most useful algorithms are implemented on the GPU. It is developed primarily at Meta's Fundamental AI Research group. News See CHANGELOG.md for detailed information about latest features. Introduction Faiss contains several methods for similarity search. It assumes that…
read the full faiss overview →
About LangWatch
Website · Docs · Discord · Self hosting Why LangWatch? The platform for LLM evaluations and AI agent testing. We help teams test, simulate, evaluate, and monitor LLM powered agents end to end — before release and in production. Built for teams that need regression testing, simulations, and production observability without building custom tooling. End to end agent simulations Run realistic scenarios against your full stack (tools, state, user simulator, judge) and pinpoint where your agents break, and why? down to each decision. Eval + observability + prompts in one loop Trace → dataset → evaluate → optimize…
read the full LangWatch overview →
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Frequently asked questions
Is faiss or LangWatch more popular?
faiss has 41,256 GitHub stars and LangWatch has 5,011. 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 (41,256 stars) or its MIT licence terms. Choose LangWatch if its feature set, stack or Apache-2.0 licence fits better. Both are self-hostable.