Phoenix

What it is for

Phoenix is a local-first AI observability desk: send OpenTelemetry traces, score spans, then rerun the same dataset as an experiment. Use it when the job is see why an agent failed and prove a fix, not when you need a YAML-only CI eval.

What makes it unique: the cover is the official Arize-ai/phoenix GitHub file list — src/, examples/, Elastic License 2.0 in the About pane — not a marketing orb.

Key features

• Tracing — one run as spans: model calls, retrieval, tools, via OTel / OpenInference (What is Phoenix; phoenix.arize.com). A log, not a score.
• Evaluation — LLM-as-judge, code checks, or labels on traces and dataset rows (docs Evaluation). A score, not a span.
• Prompt playground — version a prompt, compare variants, replay a span with new inputs (docs Prompt Engineering). An iterate, not a trace ingest.
• Datasets & experiments — collect traces or upload CSV, then rerun two app versions on the same inputs (docs Datasets & Experiments). A bench, not a live tail.
• Human annotations — attach ground truth in the UI (docs Evaluation “Human annotations”). People, not a grader.

PXI (the in-app agent) sits on this desk. phoenix serve / Docker / Helm and the Python/TS SDKs are install / SDK. Spans and storage are the meter on hosted AX. Model names are SKU.

Who it's for

Best fit: agent teams who will self-host Phoenix for $0 (uvx arize-phoenix serve) and only open Arize AX when they want a managed cloud.

Pricing

Verified 2026-10-22 (Asia/Shanghai) from phoenix.arize.com, the ELv2 LICENSE, and arize.com/pricing (AX is the hosted sister, not Phoenix itself).

• Phoenix (self-host) — Elastic License 2.0. License fee $0. Local / Docker / Kubernetes. You bring compute. Homepage: uvx arize-phoenix serve.
• AX Free — $0. No card. 25k spans / month; 1 GB ingest; 15-day retention; unlimited users and evals; SaaS.
• AX Pro — $50/month. 50k spans; 10 GB; 30-day retention; SaaS.
• AX Enterprise — custom. Custom spans/storage/retention; SaaS or self-hosted AX; SSO; HIPAA options.

Do not invent a separate “Phoenix Cloud $99” card — the public dollar table we opened is AX. Phoenix stays $0 to run yourself. ELv2 is source-available (not Apache); confirm the license if you ship a competing hosted service.

Limitations / costs

• ELv2, not Apache. Read the license before you resell a hosted Phoenix.
• AX $50 is the first paid hosted card. Phoenix itself has no seat.
• Trace desk, not a YAML eval CLI. For prompt × provider matrices in CI, see Promptfoo.

Alternatives

• Promptfoo — YAML eval + red team when you do not need OTel spans.
• Langfuse — another self-host observability UI.
• LangSmith — LangChain’s hosted trace + eval desk.

Official tutorial

Official Arize AI channel video: How To Self-Host LLM Observability & Tracing (oEmbed author: Arize AI).

Written path: What is Phoenix plus Environments and AX pricing.

Website

https://phoenix.arize.com

Repository

https://github.com/Arize-ai/phoenix

Source

Catalog row curated for AI Tools Nav. Cover is the official Arize-ai/phoenix GitHub file list (ELv2 + examples/). Phoenix self-host $0; AX hosted cards from arize.com/pricing (Free $0 / 25k spans; Pro $50 / mo). Tutorial oEmbed author: Arize AI.

Last verified

2026-10-22 (Asia/Shanghai) editorial check.