Phoenix is a free, open-source library for observability. It was designed to be used for experimentation, evaluation and troubleshooting. It allows AI engineers to visualize their data quickly, evaluate performance, track issues, and export the data to improve. Phoenix was built by Arize AI and a group of core contributors. Arize AI is the company behind AI Observability Platform, an industry-leading AI platform. Phoenix uses OpenTelemetry, OpenInference, and other instrumentation. The main Phoenix package arize-phoenix. We offer a variety of helper packages to suit specific use cases. Our semantic layer adds LLM telemetry into OpenTelemetry. Automatically instrumenting popular package. Phoenix's open source library supports tracing AI applications via manual instrumentation, or through integrations LlamaIndex Langchain OpenAI and others. LLM tracing records requests' paths as they propagate across multiple steps or components in an LLM application.