What it is
Phoenix is Arize's open tool for tracing and evaluating LLM applications. It is built on OpenTelemetry and Arize's OpenInference instrumentation, with auto-instrumentation for LlamaIndex, LangChain, DSPy, Mastra, the Vercel AI SDK, and OpenAI, Bedrock and Anthropic clients in Python, TypeScript and Java.
Beyond traces it offers LLM-as-judge and code evaluators (or ones from Ragas and DeepEval), datasets and experiments for comparing app versions, prompt versioning and a playground. It runs locally, in Docker or on Kubernetes with a Helm chart. Arize sells a managed platform, Arize AX, with a free tier of 25,000 spans a month and a $50-a-month Pro plan.
Phoenix is licensed under the Elastic License 2.0, which allows use and modification but forbids offering it to others as a hosted service. Dynatrace completed its $915 million acquisition of Arize on 1 October 2026 and says Arize will continue supporting Phoenix.
Our review
Phoenix is the tracing tool to pick when evaluation, not dashboards, is the job, and it is now a Dynatrace product. Dynatrace completed its $915 million purchase of Arize on 1 October 2026 and says Phoenix will continue to be supported. Development has not slowed: arize-phoenix 20.25.0 shipped on 23 October 2026, and the repo has about 12,000 stars.
Its foundation is open standards. Traces use OpenTelemetry and Arize's OpenInference conventions, so instrumentation is not tied to Phoenix, and in June 2026 OpenTelemetry accepted OpenInference's instrumentation code as a donation, though not its semantic conventions. A new `px setup` command detects your framework and installs the right instrumentation, and `uvx arize-phoenix serve` starts the whole app with no install.
The evaluation loop is the strength. Datasets built from traces, experiments that rerun them against new prompts or models, and evaluators from Ragas or DeepEval make it a tool for improving quality, not only watching it. Evals and experiments are unlimited on every AX plan, so the managed version does not meter the part Phoenix does best.
Defaults need attention before production. Phoenix starts with SQLite in a temporary folder, so data vanishes unless you set a working directory or PostgreSQL. Authentication is off by default and turning it on later stops trace ingestion until API keys exist. Basic UI analytics are collected unless PHOENIX_TELEMETRY_ENABLED=false, though Arize says no trace data is sent. The Elastic License 2.0 forbids offering Phoenix as a hosted service; Langfuse's MIT core and Opik's Apache 2.0 have no such clause.
Where it earns its place
A data scientist debugging a RAG chatbot on a laptop
See why retrieval returns the wrong passages
Run Phoenix locally, auto-instrument the LlamaIndex or LangChain app and inspect each retrieval span next to the answer. Free, no account, and nothing leaves the machine apart from opt-out UI analytics.
An ML platform team at a 300-person SaaS company
Self-host tracing and regression tests for four LLM features
Deploy with the Helm chart on PostgreSQL, enable PHOENIX_ENABLE_AUTH with OAuth2 or LDAP, and run experiments on trace datasets before each prompt change. No licence fee; the cost is a database and a small Kubernetes deployment.
A head of engineering already paying for Dynatrace
Decide where LLM observability should live
Phoenix covers development and evaluation free; Arize AX Pro at $50 a month adds managed storage with 30-day retention. Dynatrace says it will integrate Arize over time, which may favour consolidation but makes AX's roadmap a Dynatrace decision.
Before you commit
- Setup
- `pip install arize-phoenix && phoenix serve` (Python 3.11 to 3.14) or `uvx arize-phoenix serve`; the UI and trace endpoint share port 6006. Docker images and a Helm chart cover servers.
- Integrations
- Auto-instrumentation for LlamaIndex, LangChain, DSPy, Mastra, the Vercel AI SDK and OpenAI, Bedrock and Anthropic clients in Python, TypeScript and Java; evaluators from Ragas and DeepEval.
- Data and privacy
- Self-hosted data stays on your infrastructure and can run air-gapped; retention is unlimited by default. Auth is disabled until PHOENIX_ENABLE_AUTH and PHOENIX_SECRET are set. UI analytics are on by default; no trace data is collected. Arize's pricing page lists SOC 2 Type II and HIPAA for AX, with self-hosting and audit logs on Enterprise only.
- Cost at scale
- Self-hosting is free with no usage limits; budget a PostgreSQL instance for production. Arize AX: Free 25k spans/month, Pro $50/month for 50k spans; overage prices are not published.
- Limits
- SQLite default loses data without a persistent volume; enabling auth on a live deployment blocks ingestion until keys exist; Elastic License bars resale as a service; about 1,200 open issues and pull requests.
What's good
- Built on OpenTelemetry and OpenInference
- Datasets, experiments and evaluators in one loop
- One command (`uvx arize-phoenix serve`) to run locally
- Releases most weeks; 20.25.0 on 23 October 2026
What's not
- Elastic License 2.0, not OSI open source
- Owned by Dynatrace since October 2026
- Auth off and SQLite in a temp folder by default
- AX Free keeps data only 15 days
Best for
Engineers and data scientists who want standards-based tracing with a strong evaluation loop, starting on a laptop.
Alternatives
Arize Phoenix: common questions
- Is Arize Phoenix worth it?
- Phoenix has the strongest evaluation loop of the open tracing tools, wrapped in a licence and an owner that legal teams will want to discuss. We rate it 4.2 out of 5.
- How much does Arize Phoenix cost?
- Free to self-host under the Elastic License 2.0 (source-available; no hosting it as a service for others). Managed Arize AX: Free (25k spans/month, 15-day retention, 1 GB); Pro $50/month (50k spans, 30 days, 10 GB); Enterprise custom.
- What are the downsides of Arize Phoenix?
- Elastic License 2.0, not OSI open source; owned by Dynatrace since October 2026; auth off and SQLite in a temp folder by default; aX Free keeps data only 15 days.
- Who is Arize Phoenix best for?
- Engineers and data scientists who want standards-based tracing with a strong evaluation loop, starting on a laptop.
- How much does Arize Phoenix cost for a team or in production?
- Self-hosting is free with no usage limits; budget a PostgreSQL instance for production. Arize AX: Free 25k spans/month, Pro $50/month for 50k spans; overage prices are not published.
- Is Arize Phoenix safe for company data?
- Self-hosted data stays on your infrastructure and can run air-gapped; retention is unlimited by default. Auth is disabled until PHOENIX_ENABLE_AUTH and PHOENIX_SECRET are set. UI analytics are on by default; no trace data is collected. Arize's pricing page lists SOC 2 Type II and HIPAA for AX, with self-hosting and audit logs on Enterprise only.
- What are the best Arize Phoenix alternatives?
- The closest alternatives we have reviewed are Langfuse, Opik and Ragas.
Answers checked Oct 23, 2026.
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