LLM Observability Stack Selection
The 2026 observability market splits into two categories. Development platforms (LangSmith, Langfuse, Comet Opik) bundle monitoring with evals, prompt management, session replays. Gateway/instrumentation tools (Helicone, SigNoz, OpenLLMetry, Phoenix) focus on telemetry. Langfuse is MIT-licensed core with strong OSS balance (50K events/month free cloud). Phoenix is OpenTelemetry-native under Elastic License 2.0 — excellent for drift/RAG visualization, not a persistent production backend. Arize AX uses zero-copy Iceberg/Parquet integration claiming 100x cheaper than monolithic observability. LangSmith leads for LangChain/LangGraph, $39/user/mo, self-host in Enterprise only. Helicone is proxy-based with 15-30 min setup, 100K req/mo free, but less depth on agent traces. Common production pattern: Gateway (Helicone/Portkey) + eval platform (Phoenix/TruLens) glued by OpenTelemetry. Distinguish development platforms (bundled: evals + prompts + sessions) from gateway/telemetry tools (traces + metrics only). Map six major tools (Langfuse, LangSmith, Phoenix, Arize AX, Helicone, Opik) to their licensing, pricing, and sweet-spot use cases. Explain the OpenTelemetry-glue pattern that lets you combine a gateway tool with a separate eval platform. Name the 2026 cost differentiator (Arize AX's zero-copy approach vs monolithic ingest) and state the rough 100x multiplier. You shipped an LLM feature. It works. You have no visibility into prompt failures, tool loops, latency regressions, cost spikes, or prompt-cache hit rate. You Google "LLM observability" and get eight tools all claiming they solve the same problem at three different…
LLM Observability Stack Selection: The 2026 observability market splits into two categories. Development platforms (LangSmith, Langfuse, Comet Opik) bundle…
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