Arize AX vs Arize Phoenix
Both are observability & tracing tools. Here is how they actually differ on price, billing model and deployment.
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.
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.
| Arize AX | Arize Phoenix | |
|---|---|---|
| Category | Observability & Tracing | Observability & Tracing |
| Our rating | 4/5 | 4/5 |
| Starting price | $50/mo | $0 |
| Billing meter | span | No usage metering |
| Free plan | Yes | Yes |
| Free self-hosting | No or paid tier only | Yes, free |
| Best for | 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. | 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 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 →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 Arize AX and Arize Phoenix?
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. 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, Arize AX or Arize Phoenix?
It depends entirely on your workload shape, because they meter differently - Arize AX bills on span and Arize Phoenix bills on no usage metering. Published starting prices are $50/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 Arize AX or Arize Phoenix?
Arize AX: No or paid tier only. Arize Phoenix: Yes, free. Free self-hosting means no licence fee, not no cost - you still own the infrastructure, upgrades and on-call.