Langfuse vs Arize Phoenix: License, Self-Hosting and Tracing

Langfuse and Arize Phoenix are self-hostable LLM observability platforms that accept OpenTelemetry traces but differ substantially in licensing, deployment complexity, evaluation workflows, and ownership. Langfuse, which joined ClickHouse in January 2026, provides an MIT-licensed core with enterprise-only directories and requires a six-service stack including ClickHouse, PostgreSQL, Redis, and MinIO; it supports HTTP OTLP ingestion, maps many OpenInference attributes, and can run LLM-as-a-judge evaluations continuously on live production observations. Phoenix, developed by Arize before its acquisition by Dynatrace in October 2026, uses the Elastic License 2.0 for its server and Apache 2.0 for certain client packages, can run as a single process or container with SQLite or PostgreSQL, supports both HTTP and gRPC OTLP, and focuses server-side evaluators on saved datasets and experiments rather than live traffic. Both platforms support tracing, prompt versioning, evaluations, and agent-tool-call records, although traces only report what the agent emitted rather than independently proving real-world effects. The comparison also distinguishes Phoenix from Arize AX, a separate managed commercial product, and presents TestMu AI Agent Assurance as a staging-focused tool that verifies an agent’s actual file changes, tool use, and external records before release.

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