Arize Phoenix is actually already open source — a free LLM observability and evaluation library built on OpenTelemetry, self-hostable in one command or run locally in a notebook. Arize AI (the company behind it) also sells a separate hosted enterprise platform, but the Phoenix project itself carries no proprietary lock-in.
Langfuse sits in the same open-source LLM-observability space, with a different focus on prompt management and cost tracking alongside tracing. Since Phoenix is already free and open, the choice between them comes down to whether you want Phoenix's OpenTelemetry-native tracing or Langfuse's broader prompt-management and cost-tracking feature set.
FAQ
Is there a free, open-source alternative to Arize Phoenix?
Arize Phoenix is already open source and free to self-host. Langfuse is another MIT-licensed option in the same space if you want built-in prompt management and cost tracking alongside tracing.
What's the best open-source alternative to Arize Phoenix?
Since Phoenix itself is already open source, the real comparison is feature focus: Langfuse adds prompt management and cost tracking that Phoenix's OpenTelemetry-native tracing doesn't emphasize.
What are the top open-source alternatives to Arize Phoenix?
Browse all open-source alternatives to Arize Phoenix above, or explore the full Analytics category for more options.