Arize Phoenix Review 2026

Arize Phoenix is an open-source AI observability and evaluation platform for tracing, testing, and improving LLM applications and agents.

Arize Phoenix is an open-source AI observability and evaluation platform for tracing, testing, and improving LLM applications and agents. It uses OpenTelemetry-compatible tracing, supports datasets and experiments, runs evaluations, and includes a Prompt IDE for examining and iterating on prompts. The key distinction is deployment flexibility: a developer can run Phoenix locally or self-host the open-source project, while teams wanting managed storage, issue detection, and collaboration can use Arize AX. This makes Phoenix attractive to builders who want an instrumentation path that does not begin with a mandatory SaaS contract.

Arize's September 2026 pricing page lists AX Free at $0 with 25,000 trace spans per month, 1 GB monthly ingestion, 15-day retention, unlimited users, and unlimited evaluations. AX Pro costs $50 per month and raises the allowance to 50,000 spans, 10 GB ingestion, and 30-day retention while keeping unlimited users and evaluations. Enterprise pricing is custom, with unlimited issue signals, custom spans, ingestion, and retention, plus SaaS or self-hosted deployment. Open-source Phoenix can be self-hosted without a license fee, although infrastructure, backups, upgrades, and operational labor remain real costs.