AI Agent Observability 2026: Braintrust vs Arize Phoenix vs Langfuse Compared
The fastest-moving part of AI infrastructure in 2026 is observability — and for good reason. The LLM observability platform market hit $2.69B this year (up from $1.97B in 2025), growing at a 36.3% CAGR. Three platforms dominate production use: Braintrust (SaaS-only, $80M Series B, enterprise-grade CI/CD gates), Arize Phoenix (100% open-source, OpenTelemetry-native, 9,100+ GitHub stars), and Langfuse (MIT-licensed, ClickHouse-acquired, 19,000+ GitHub stars). Choosing the wrong one means either paying for features you won’t use or hitting invisible ceilings when your agent fleet scales. ...