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

LLM observability and evaluation platforms are tools that record and assess what large language model applications do in production, capturing every step from user input through model responses and tool calls. These platforms matter because traditional software monitoring fails to detect semantic failures, where outputs can be technically valid but factually wrong, hallucinated, or irrelevant. The market has split into four types of solutions: AI-native observability platforms that treat LLM traces as primary objects, open-source evaluation libraries that score output quality, AI gateways that proxy requests between applications and models, and traditional application monitoring tools extended with LLM tracing. A vendor-neutral standard called OpenTelemetry GenAI semantic conventions now connects these different approaches, allowing teams to instrument their systems once and reduce dependency on any single vendor.