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Phoenix

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Evaluate, experiment, and optimize AI products in real time with open-source LLM tracing.

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Tracked since2026
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The Bottom Line

Entry price

Free plan available, paid tiers above

Biggest pro

Open-source and self-hostable, offering flexibility and no vendor lock-in.

Biggest con

Advanced features like dedicated support and custom data limits are only available in higher-tier paid plans.

TL;DR - Phoenix

  • Open-source LLM tracing and evaluation platform.
  • Provides real-time visibility, debugging, and optimization for AI products.
  • Features interactive prompt playgrounds, evaluation libraries, and dataset visualization.
Pricing: Free plan available
Best for: Growing teams

What is Phoenix?

Editorial review
Phoenix is an open-source platform designed for evaluating, experimenting with, and optimizing AI products, specifically Large Language Models (LLMs). It provides comprehensive LLM observability by allowing users to trace, visualize, and debug LLM applications in real-time. Built on OpenTelemetry, Phoenix offers seamless data collection, transparency, and avoids vendor lock-in. The tool is ideal for AI engineers, developers, and data scientists working with LLMs who need to understand model behavior, identify failures, and improve performance. It helps in debugging complex LLM decision-making, flagging poor responses, and troubleshooting issues related to retrieval and tool execution. Phoenix aims to integrate observability directly into the development process, encouraging continuous improvement of LLM applications before and after deployment. Key functionalities include interactive prompt playgrounds for iteration, streamlined evaluation libraries with pre-built templates and human feedback integration, and dataset clustering/visualization to uncover performance issues using embeddings. Its open-source nature and self-hostable option provide flexibility and control for small teams to large enterprises.

Available on: Web

Pros & Cons

Pros

  • Open-source and self-hostable, offering flexibility and no vendor lock-in.
  • Provides deep observability into LLM behavior and decision-making.
  • Facilitates rapid experimentation and iteration with interactive playgrounds.
  • Supports both automated and human feedback for comprehensive evaluations.
  • Strong community support and integrations with popular LLM frameworks.

Cons

  • Advanced features like dedicated support and custom data limits are only available in higher-tier paid plans.
  • The free SaaS tier has limited trace spans and ingestion volume.
  • Requires some technical expertise for self-hosting and full utilization.

Preview

Key Features

OpenTelemetry (OTEL) for seamless setup and data collectionApplication tracing for total visibility into LLM app dataInteractive prompt playground for prompt and model iterationStreamlined evaluation and annotation library with pre-built templatesDataset clustering and visualization using embeddingsSelf-hostable with no feature gates or restrictionsIntegration with various LLM tools and frameworksOnline and offline evaluations, including LLM as judge and code evals

Pricing Plans

Phoenix Small teams and smaller data

Free & open source

  • Trace spans user managed
  • Ingestion volume user managed
  • Projects user managed
  • Retention user managed
  • Support add-on dedicated support

AX Free

Free

  • 25k trace spans per month
  • 1 GB ingestion volume per month
  • 7 days retention
  • Alyx (Arize agent)
  • Online evals
  • Product observability (monitors & custom metrics)
  • Community support

AX Pro

$50 per month

  • 50k trace spans per month
  • 10 GB ingestion volume per month
  • 15 days retention
  • Everything in AX Free
  • Higher rate limits
  • Longer retention
  • Email support

AX Enterprise

Custom

  • Custom trace spans
  • Custom ingestion volume
  • Custom projects
  • Configurable retention
  • Everything in AX Pro
  • Dedicated support
  • Uptime SLA
  • Custom data limits
  • SOC2 reports and HIPPA
  • Training sessions
  • DataFabric Connect
  • Self-Hosting add-on
  • Data residency
  • Multi-region deployments

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Phoenix FAQ

What is Phoenix?

Phoenix is an open-source LLM tracing and evaluation platform that helps AI engineers and developers evaluate, experiment with, and optimize their AI products in real time. It provides tools for visualizing LLM decision-making, debugging failures, and improving model performance.

How much does Phoenix cost?

Phoenix offers a freemium model. The core Phoenix is open-source and self-hostable for free. The SaaS offering, Arize AX, has a free tier (AX Free) with limited usage, a paid tier (AX Pro) starting at $50 per month, and a custom Enterprise plan.

Is Phoenix free?

Yes, Phoenix is free as an open-source, self-hostable solution. Additionally, there is a free SaaS tier called Arize AX Free, which includes 25k trace spans and 1 GB ingestion volume per month with 7 days retention.

Who is Phoenix for?

Phoenix is designed for AI engineers, developers, and data scientists who are building, evaluating, and optimizing applications powered by Large Language Models (LLMs). It's suitable for individuals, startups, and enterprises looking for robust LLM observability and evaluation tools.