Arize Phoenix vs Langfuse
Prices and features checked 2026-10-17 on both vendors' own pages. “not verified” means we could not confirm it.
Arize Phoenix or Langfuse? Both can be self-hosted from public code. Phoenix is under the Elastic License 2.0; Langfuse's core is MIT. For managed hosting, Arize sells Arize AX (free tier with 25k spans, Pro at $50/month for 50k spans) and Langfuse sells Langfuse Cloud (Hobby free with 50k units, Core at $29/month with 100k units). Both are OpenTelemetry-based and offer LLM-as-judge evals, human annotation and prompt versioning.
| Arize Phoenix | Langfuse | |
|---|---|---|
| Made by | Arize AI | Langfuse (ClickHouse, Inc.) |
| Licence | Phoenix: Elastic License 2.0. Arize AX: hosted service [source] | MIT for code outside the ee/ directories; ee/ code under a separate licence [source] |
| Self-hosting | Phoenix self-hosts; AX self-hosted only on Enterprise [source] | Free to self-host (Docker Compose or Kubernetes) [source] |
| Meter | Trace spans and ingestion volume (GB) [source] | Billable units: traces, observations (spans, events, generations) and scores [source] |
| Free tier | AX Free: 25k spans/month, 1 GB ingestion, 15-day retention, unlimited users [source, checked 2026-10-17] | Hobby: 50k units/month, 30 days data access, 2 users [source, checked 2026-10-17] |
| Entry paid price | AX Pro $50/month: 50k spans, 10 GB, 30-day retention (overage rates not stated on the pricing page) [source, checked 2026-10-17] | Core $29/month: 100k units included, then $8 per 100k units (graduated down to $6 per 100k above 50M) [source, checked 2026-10-17] |
| Retention | 15 days (AX Free), 30 days (AX Pro), custom on Enterprise [source] | Data access: 30 days (Hobby), 90 days (Core), 3 years (Pro and Enterprise) [source] |
| OpenTelemetry | OpenTelemetry compliant on all AX plans [source] | OpenTelemetry ingestion on all plans [source] |
| CI gating | Experiments as regression gates in CI/CD [source] | Run experiments in CI and gate changes [source] |
| LLM-as-judge | Online and offline evals, agent-as-a-judge [source] | LLM-as-judge evaluators on all plans [source] |
| Human annotation | Human annotations and feedback [source] | Annotation queues: 1 on Hobby, 3 on Core, unlimited on Pro [source] |
| Prompt management | Prompt serving and versioning [source] | Prompt versioning and release labels [source] |
| Dataset versioning | not verified | Dataset versions are accessible via the SDK/API [source] |
| SOC 2 / HIPAA | SOC 2 Type II on paid AX plans; HIPAA on Enterprise [source] | SOC 2 Type II and ISO 27001 reports and HIPAA (BAA) on Pro ($199/month) and Enterprise [source] |
Verdict: when to use which
Use Arize Phoenix if you want an OpenTelemetry/OpenInference-first tool and may later move to Arize AX for online evals and agent features.
Use Langfuse if you want an MIT-licensed core, prompt management with release labels, and a cloud plan with unlimited users and published per-unit overage rates.
The meters differ, so price both on a week of your own traffic in the pricing calculator.
FAQ
What is the licence difference?
Phoenix uses the Elastic License 2.0, which is source-available with limits on offering it as a managed service. Langfuse code outside its ee/ directories is MIT; ee/ code is under a separate licence.
Which cloud plan publishes overage rates?
Langfuse: $8 per 100k units above 100k, graduated down to $6. Arize AX Pro: the pricing page lists allowances (50k spans, 10 GB) but not overage rates.
SOC 2 and HIPAA?
Arize lists SOC 2 Type II on paid AX plans and HIPAA on Enterprise. Langfuse lists SOC 2 Type II and HIPAA on Pro and Enterprise.
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