Langfuse vs Phoenix (Arize)
Both are alternatives to LangSmith. Here's how they stack up — verified facts, no spin.
Also searched as Phoenix (Arize) vs Langfuse — same comparison, one verdict.
Langfuse is open source (MIT Expat (core); ee/ directories under a separate enterprise licence) 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.
Langfuse
TOP PICKThe self-hosted default for LLM tracing — MIT core, framework-agnostic.
Langfuse is the most widely adopted open LLM observability platform: tracing, evaluation, prompt management and cost tracking, deployable with Docker on your own infrastructure so traces containing customer data never leave your network. It is deliberately framework-agnostic — LangChain, LlamaIndex, the provider SDKs directly, or OpenTelemetry — which makes it the natural exit from a LangChain-shaped tool. At 32k stars with commits landing daily it is the healthiest project in this category. Licensing needs precision: the core is MIT Expat, while the ee/ directories carry a separate enterprise licence.
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
10 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.
| Langfuse | Phoenix (Arize) | |
|---|---|---|
| Sovereignty ScoreOur transparent 0–100 composite for data ownership and exit cost. | 90 | 62 |
| Open source | Yes | No |
| Self-hostable | Yes | Yes |
| Local-first data | Yes | Yes |
| License | MIT Expat (core); ee/ directories under a separate enterprise licence | Elastic License 2.0 (source-available, not OSI open source) |
| Pricing | Free to self-host — Docker Compose or Kubernetes, costs are your own infrastructure. A managed cloud with a free tier and paid plans exists if you would rather not run it. | Free to self-host under ELv2 for your own internal use. Arize's commercial platform is priced separately. |
| RAM to run it wellThe figure that actually matters, not the vendor's minimum. | 4 GB | — |
| Realistic running costWhat the box costs each month if you run it yourself. | $24–40/mo plus Postgres and ClickHouse, against per-trace observability pricing | — |
| Setup timeHonest first-install estimate, not the marketing quickstart. | 2 hours | — |
| Ongoing maintenanceThe part nobody budgets for. | Moderate. Five components, and trace volume grows faster than teams expect. | — |
Langfuse is Macrostack's recommended LangSmith alternative, so it's our pick here.
Weighing both against staying on LangSmith? Is LangSmith free? What it actually costs →
Langfuse
Strengths
- +Self-hosted: prompts and completions stay inside your network
- +Framework-agnostic — not tied to any one orchestration library
- +Tracing, evals, prompt management and cost tracking in one tool
- +32k stars and daily commits — the most active project in this category
Trade-offs
- −Self-hosting means running Postgres, ClickHouse and the collector yourself
- −The MIT core stops at the ee/ directories; SSO and some enterprise features sit behind a separate licence
- −Evaluation tooling is less polished than LangSmith's if you live inside LangChain
- −Trace storage grows fast — retention policy is your problem to plan
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 Langfuse
if you want the source and the option to fork it, and self-hosted: prompts and completions stay inside your network.
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 — self-hosting means running Postgres, ClickHouse and the collector yourself, 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.
What it takes to run these yourself
Real requirements and honest running costs, not the vendor quickstart.
Langfuse vs Phoenix (Arize) — common questions
Is Langfuse a better fit than Phoenix (Arize) for llm observability & evaluation?
It depends on what you are optimising for, and the honest split is this: Langfuse scores 90 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?
Langfuse 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 Langfuse 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 Langfuse 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.
Related alternative guides
Facts verified 2026-07-30. Licenses and pricing change — spotted something out of date? That's a correction we want.