Langfuse stands out as the premier open-source LLM observability platform in late 2025, delivering end-to-end tracing, prompt management, evaluations, and metrics for production-grade applications. Its OpenTelemetry foundation, vast integrations, and full self-hosting capability provide unmatched flexibility and data sovereignty—trusted by enterprises and developers alike.

LangSmith remains the premier observability and evaluation platform for LLM applications in late 2025. It delivers unmatched tracing, debugging, testing, and monitoring—working seamlessly with LangChain or any framework, with zero added latency.

TruLens remains the premier open-source framework for LLM evaluation in late 2025, offering powerful feedback functions for relevance, groundedness, bias, and custom metrics, plus full OpenTelemetry tracing. It excels at RAG and agent workflows, enabling objective benchmarking and production monitoring—completely free with strong community support from Snowflake.