Langfuse

Open-source LLM observability and evaluation platform. Python SDK provides tracing via @observe decorator, OpenTelemetry integration, and a low-level client for manual trace/span management. Works with any LLM framework — not tied to LangChain. Self-hostable (Docker/Kubernetes) or cloud (EU/US regions). MAJOR VERSION NOTE: SDK was completely rewritten in v3 (released June 2025). v3 is OpenTelemetry-based with a new singleton client pattern. All v2 import paths, class names, and initialization patterns are broken in v3. pip install langfuse installs v3 as of Feb 2026.