OpenLLMetry vs Phoenix (Arize)
Both are alternatives to LangSmith. Here's how they stack up — verified facts, no spin.
Also searched as Phoenix (Arize) vs OpenLLMetry — same comparison, one verdict.
OpenLLMetry is open source (Apache-2.0) and Phoenix (Arize) is not (Elastic License 2.0 (source-available, not OSI open source)) — so the real question is whether you want to own the llm observability & evaluation stack or rent it.
OpenLLMetry
Apache-2.0 OpenTelemetry instrumentation — send traces anywhere you already send them.
OpenLLMetry takes the opposite approach to a platform: it is a set of Apache-2.0 OpenTelemetry extensions that emit LLM traces in a standard format, so they flow into whatever you already run — Grafana, Datadog, Honeycomb, Jaeger or Traceloop's own hosted backend. If you already have observability infrastructure, this adds LLM visibility to it rather than asking you to adopt a second, parallel system. It is also the strongest hedge against lock-in: standard telemetry moves between backends by configuration.
Phoenix (Arize)
Strong evaluation tooling — but read the licence before you build on it.
Phoenix is Arize's tracing and evaluation tool, and its evaluation workflow is among the best available: run experiments, score outputs against datasets, and inspect where a chain went wrong. It runs locally in a notebook or as a self-hosted service. The critical detail most listicles omit is the licence — Phoenix is Elastic License 2.0, which is source-available rather than open source. You may use and modify it, but you may not offer it to third parties as a hosted or managed service, and you may not circumvent its licence-key functionality.
Side by side
6 points of comparison, every one read from a verified field. Green marks the side that wins a row outright. A dash means we do not hold that fact — never that it is zero.
| OpenLLMetry | Phoenix (Arize) | |
|---|---|---|
| Sovereignty ScoreOur transparent 0–100 composite for data ownership and exit cost. | 92 | 62 |
| Open source | Yes | No |
| Self-hostable | Yes | Yes |
| Local-first data | Yes | Yes |
| License | Apache-2.0 | Elastic License 2.0 (source-available, not OSI open source) |
| Pricing | Free — Apache-2.0 instrumentation libraries. You pay only whatever backend you already send telemetry to; a hosted Traceloop backend is available separately. | Free to self-host under ELv2 for your own internal use. Arize's commercial platform is priced separately. |
OpenLLMetry edges it on the Sovereignty Score, but the right pick depends on the trade-offs below.
Weighing both against staying on LangSmith? Is LangSmith free? What it actually costs →
OpenLLMetry
Strengths
- +Apache-2.0 throughout — no enterprise-directory carve-out
- +Standard OpenTelemetry: traces go to a backend you already operate
- +The best protection against lock-in — switching backends is configuration
- +Reuses your existing observability stack instead of adding a parallel one
Trade-offs
- −Instrumentation, not a platform — no evaluation or prompt-management UI
- −You need a trace backend already, or you are choosing one anyway
- −Generic backends render LLM traces less legibly than a purpose-built UI
- −Smaller project (about 7k stars) than Langfuse
Phoenix (Arize)
Strengths
- +Excellent evaluation and experiment tooling — the strongest of this group
- +Runs locally, including straight from a notebook
- +Self-hostable, so traces stay in your infrastructure
- +Actively developed, with commits landing daily
Trade-offs
- −Elastic License 2.0 — source-available, NOT open source; you cannot offer it as a managed service
- −The licence restriction is a real constraint if your product is itself a platform
- −Score of 62 reflects the licensing limitation, not the engineering quality
- −Smaller community than Langfuse
Which one fits you
The trade-offs above, turned into a decision. Find the line that describes your team.
Choose OpenLLMetry
if you want the source and the option to fork it, and apache-2.0 throughout — no enterprise-directory carve-out.
Choose Phoenix (Arize)
if excellent evaluation and experiment tooling — the strongest of this group.
Neither, yet
if both carry a real cost you should weigh first — instrumentation, not a platform — no evaluation or prompt-management UI, and elastic License 2.0 — source-available, NOT open source; you cannot offer it as a managed service. If either of those is a dealbreaker for your team, the shortlist is wrong rather than the choice.
OpenLLMetry vs Phoenix (Arize) — common questions
Is OpenLLMetry a better fit than Phoenix (Arize) for llm observability & evaluation?
It depends on what you are optimising for, and the honest split is this: OpenLLMetry scores 92 to Phoenix (Arize)'s 62 on data ownership and exit cost, so it is the safer choice if you care about being able to leave. Phoenix (Arize) earns its place on a different axis — excellent evaluation and experiment tooling — the strongest of this group. Neither is a wrong answer for every team; the table above is the actual comparison.
What happens if we want to switch later?
OpenLLMetry keeps its data local or in open formats, so leaving is an export rather than a negotiation. Phoenix (Arize) is still self-hostable, so the files stay on your server either way — but it is not local-first by design, so check what its export produces before you rely on it.
Can I self-host OpenLLMetry or Phoenix (Arize)?
Both can be self-hosted. The difference is what it costs you in time rather than whether it is possible — see the setup and maintenance rows above.
Are OpenLLMetry and Phoenix (Arize) both alternatives to LangSmith?
Yes — both appear in our LangSmith comparison, which is why they are worth putting side by side. People usually arrive here already having decided to move off LangSmith and now choosing between the two replacements, which is a narrower and much easier question.
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Facts verified 2026-07-30. Licenses and pricing change — spotted something out of date? That's a correction we want.