Langfuse
Open-source or cloud-hosted. Strong on tracing, prompt management, evaluation. Free tier generous. Good fit for teams wanting vendor-neutral stack and cost control.
Portkey
Focus on gateway, reliability, routing across multiple LLM providers. Strong for multi-model strategies where you need fallbacks, A/B testing, cost optimization at the API level.
LangSmith
From LangChain. Tight integration if you use LangChain framework. Trace, evaluate, prompt management integrated. Commercial; pricing scales with volume.
Decision
Open-source preference: Langfuse. Multi-model routing focus: Portkey. LangChain-native stack: LangSmith. Many teams use combinations — Portkey for gateway, Langfuse for tracing, separate evaluation tooling.