Langfuse vs Arize AX
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 AX
The commercial cloud product from the makers of Phoenix. The upgrade from free Phoenix is not a tier change - it is a repricing onto per-span billing, and online monitoring is the feature that forces it.
| Langfuse | Arize AX | |
|---|---|---|
| Category | Observability & Tracing | Observability & Tracing |
| Our rating | 5/5 | 4/5 |
| Starting price | $29/mo | $50/mo |
| Billing meter | event | span |
| Free plan | Yes | Yes |
| Free self-hosting | Yes, free | No or paid tier only |
| Best for | Teams that want an open-source observability platform they can self-host without losing features | Teams that outgrew self-hosted Phoenix and want the managed version without operating it, mixed ML and GenAI shops that need computer vision and model observability in the same platform, and regulated teams needing HIPAA. |
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 AX
Arize AX is the managed, production-grade half of a genuinely good two-product strategy, and the honest way to evaluate it is to understand what forces the move from free Phoenix. It is not scale, and it is not support. It is online monitoring. The open-source Phoenix build does not include online monitoring or online evaluations as part of its observability stack, so the moment you need to evaluate live production traffic rather than debug locally, you are buying AX. That is a defensible commercial line, and Arize is more upfront about it than most, but it means Phoenix is best understood as an excellent development and debugging tool rather than a complete production platform. AX itself is strong - genuinely mature ML and computer vision observability inherited from Arize's older business, online evals, and pricing that scales on spans rather than seats, which is unusually favourable for large teams. The catch is that per-span billing punishes agent workloads, and the jump from $50 a month to a reported median Enterprise spend near $60,000 a year is a cliff with nothing published in between.
Full Arize AX review →Frequently Asked Questions
What is the main difference between Langfuse and Arize AX?
Langfuse: Teams that want an open-source observability platform they can self-host without losing features Arize AX: Teams that outgrew self-hosted Phoenix and want the managed version without operating it, mixed ML and GenAI shops that need computer vision and model observability in the same platform, and regulated teams needing HIPAA. 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 AX?
It depends entirely on your workload shape, because they meter differently - Langfuse bills on event and Arize AX bills on span. Published starting prices are $29/mo and $50/mo 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 AX?
Langfuse: Yes, free. Arize AX: No or paid tier only. Free self-hosting means no licence fee, not no cost - you still own the infrastructure, upgrades and on-call.