Langfuse vs Arize Phoenix
Both are observability & tracing tools. Here is how they actually differ on price, billing model and deployment.
Langfuse
The open-source LLM observability default. Free, MIT-licensed, genuinely feature-complete when self-hosted - now a ClickHouse subsidiary after its January 2026 acquisition.
Arize Phoenix
The default open-source choice for LLM tracing and eval - runs locally in under a minute, built on OpenTelemetry. The catch is the license - the server is Elastic License 2.0, source-available, not OSI open source.
| Langfuse | Arize Phoenix | |
|---|---|---|
| Category | Observability & Tracing | Observability & Tracing |
| Our rating | 5/5 | 4/5 |
| Starting price | $29/mo | $0 |
| Billing meter | event | No usage metering |
| Free plan | Yes | Yes |
| Free self-hosting | Yes, free | Yes, free |
| Best for | Teams that want an open-source observability platform they can self-host without losing features | Teams that want fast, framework-agnostic OSS tracing and strong RAG eval, and who are not reselling Phoenix as a hosted service |
Our verdict on Langfuse
The open-source default for good reason - self-hosting is free and doesn't cripple the product, and it's dramatically cheaper than LangSmith at scale. The catch is operational, not commercial - the v3 architecture is four services now, and the migration bites. If you have the ops capacity, nothing else in the category gives you this much for free.
Full Langfuse review →Our verdict on Arize Phoenix
The default open-source pick for good reasons - it starts in under a minute, the RAG eval is the best around, and it is built on OpenTelemetry so you are not locked to one framework. Just read the license before you build a business on it. The server is Elastic License 2.0, source-available rather than OSI open source, which only bites if you plan to offer Phoenix as a service - but it is not what "fully open source" implies.
Full Arize Phoenix review →Frequently Asked Questions
What is the main difference between Langfuse and Arize Phoenix?
Langfuse: Teams that want an open-source observability platform they can self-host without losing features Arize Phoenix: Teams that want fast, framework-agnostic OSS tracing and strong RAG eval, and who are not reselling Phoenix as a hosted service Both sit in Observability & Tracing, so the decision usually comes down to billing model and deployment rather than raw capability.
Which is cheaper, Langfuse or Arize Phoenix?
It depends entirely on your workload shape, because they meter differently - Langfuse bills on event and Arize Phoenix bills on no usage metering. Published starting prices are $29/mo and $0 respectively, but those numbers are not comparable until you apply them to the same traffic. Use our cost calculator to model both against your own request volume and span count.
Can I self-host Langfuse or Arize Phoenix?
Langfuse: Yes, free. Arize Phoenix: Yes, free. Free self-hosting means no licence fee, not no cost - you still own the infrastructure, upgrades and on-call.