Tools/Arize-ai/phoenix

phoenix

AI Observability & Evaluation

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The Lens

By Erik Loyd, SaaS CEO and former COO/CFO of an AWS Premier Partner.

Updated Aug 2026

Phoenix is how you see why an LLM feature misbehaved. It traces every model call your app makes, captures the prompts and responses, and lets you score outputs with evals so you can tell whether last week's prompt change helped or hurt. Arize built it on OpenTelemetry, and it runs in a notebook, a Docker container, a Kubernetes cluster, or one of two hosted Phoenix Cloud instances Arize hands you for free.

Self-hosting is the point and there are no feature gates. Deploy it with Docker, Helm, Kubernetes, CloudFormation, Cloud Run, Railway, Render, or the CLI, point your app's tracing at it, and you get traces, datasets, experiments, and prompt management in one UI with nothing leaving your infrastructure. That matters when your prompts carry customer data you cannot ship to a vendor. It is a real service to keep running, not a library you import.

Solo developers and small teams: self-host it, or take the two free cloud instances and skip the ops entirely. Arize AX is the managed version: free at 25,000 spans a month with 15-day retention, $50/mo for 50,000 spans and 30 days, custom above that, with unlimited users on every tier because billing runs on spans and storage, not seats. Want a permissive license instead? langfuse/langfuse is MIT at its core.

The catch is that license. Phoenix is Elastic License 2.0, which is source-available, not open source. Self-host it, modify it, run your business on it, all fine. What you cannot do is turn around and sell it as a hosted service. For anyone debugging their own app that line never gets close, but do not call it MIT.

Free vs Self-Hosted vs Paid

source available

Free

Self-hosted Phoenix is free with no feature gates, no seat limits, and no usage caps. Tracing, evals, datasets, experiments, and prompt management are all in the open release under the Elastic License 2.0.

Arize also gives you 2 hosted Phoenix Cloud instances free if you would rather not run it yourself.

Cloud Pricing

Arize AX is the managed platform:

AX Free: $0, 25,000 trace spans/mo, 1 GB storage, 15-day retention
AX Pro: $50/mo, 50,000 trace spans/mo, 10 GB storage, 30-day retention
AX Enterprise: custom volume and pricing, SaaS or self-hosted deployment, adds managed agents and Data Fabric

Every tier includes unlimited users, evals, experiments, and human annotation. Billing is driven by spans and storage together, so watch both numbers, not just one.

Self-Hosted Costs

A container plus a database. Postgres 14+ is the production path via PHOENIX_SQL_DATABASE_URL; SQLite works with a persistent volume for smaller setups. Budget roughly $20 to $50/mo for a small always-on VM or Cloud Run service, plus storage that grows with trace volume (a chatty agent produces spans fast).

Pin the image tag. Arize's own deployment docs tell you to pin a specific version rather than run latest in production, and Phoenix ships often enough that this matters: 20.0.0, 20.1.0, 20.2.0, and 20.2.1 all landed between August 11 and 14, 2026.

When to Pay

Pay for Arize AX when your span volume outruns the free tiers, when you need retention past 30 days, or when you want somebody to call at 2am. The $50/mo Pro tier is cheap next to an engineer maintaining a container and a Postgres instance.

Stay self-hosted when your prompts contain data that cannot leave your network, or when you already run containers and Postgres and adding one more service is not the hard part.

Free and ungated to self-host, plus 2 free hosted Phoenix Cloud instances. Arize AX starts free and hits $50/mo at 50,000 spans. Source-available under Elastic 2.0, not open source, which only bites if you plan to resell it.

What to do by team size

Solo: free; take one of the two free Phoenix Cloud instances and skip the ops entirely
Small team: free; self-host the container or stay on free cloud, AX Free covers 25,000 spans a month
Medium team: free to self-host; move to AX Pro at $50/mo when span volume or 30-day retention justifies it
Large team: AX Enterprise if you want scale, retention, and support; self-hosted Phoenix still fits when prompts cannot leave your network

Self-hosting ops:moderate

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