Top LLM Observability and Evaluation Platforms in 2026: Langfuse, LangSmith, Braintrust, Arize, and More Compared

LLM applications fail in ways traditional software does not because the same prompt can produce different outputs and semantic errors go undetected. LLM observability and evaluation platforms record every span of an LLM pipeline and score outputs for quality. The market is growing, with the LLM observability platform market at $2.69 billion in 2026 and projected to reach $9.26 billion by 2030. The article compares platforms across tracing depth, evaluation capability, and production monitoring, noting that 57% of professionals now run agents in production. The category is structured into four camps: AI-native observability platforms, open-source evaluation libraries, AI gateways, and APM extensions. OpenTelemetry GenAI semantic conventions are a standard connecting all camps. The leading platforms include Langfuse, LangSmith, Braintrust, Arize, and MLflow, each with strengths in different areas.