Arize Phoenix

Arize Phoenix is a free, open-source LLM observability platform that gives developers full-stack visibility into LLM applications — tracing requests, evaluating outputs, and debugging RAG pipelines — without requiring a cloud subscription or vendor account. It runs locally in a Python process or scales to Docker and Kubernetes for production deployments. What Is Arize Phoenix and Why It Matters in 2026 Arize Phoenix is an open-source observability platform built specifically for LLM applications, agents, and retrieval-augmented generation (RAG) pipelines. Unlike generic APM tools, Phoenix understands LLM-native concepts — spans, traces, embeddings, prompts, retrieved contexts, and model outputs — and surfaces them in a UI designed for AI engineers. As of 2026, Phoenix has surpassed 9,000 GitHub stars, making it one of the most-adopted open-source observability tools in the AI ecosystem. The platform is backed by Arize AI but released under a permissive open-source license, meaning you can run it entirely on your own infrastructure with no usage caps or feature gating. ...

The fastest-moving part of AI infrastructure in 2026 is observability — and for good reason. The LLM observability platform market hit $2.69B this year (up from $1.97B in 2025), growing at a 36.3% CAGR. Three platforms dominate production use: Braintrust (SaaS-only, $80M Series B, enterprise-grade CI/CD gates), Arize Phoenix (100% open-source, OpenTelemetry-native, 9,100+ GitHub stars), and Langfuse (MIT-licensed, ClickHouse-acquired, 19,000+ GitHub stars). Choosing the wrong one means either paying for features you won’t use or hitting invisible ceilings when your agent fleet scales. ...