Who this is for: platform and infrastructure leads, ML engineers, and AI engineering managers choosing an observability + evaluation stack for production LLM and agent applications. You are comparing tools against real constraints — data residency, existing OTel pipelines, eval maturity, cost visibility — and you need a decision, not a listicle.
The matrix
Capabilities reflect each tool's documented feature surface as of publication. ✓ = yes, ~ = partial / via integration, — = no. Verify against current docs before committing — these products ship fast.
| Tool | Request tracing | LLM-as-judge eval | Cost / token tracking | Drift / regression detection | Self-hostable | OpenTelemetry-compatible | Notes |
|---|---|---|---|---|---|---|---|
| Arize Phoenix | ✓ | ✓ | ~ | ~ | ✓ | ✓ | Open-source LLM tracing + eval; OTel-native. |
| Langfuse | ✓ | ✓ | ✓ | ~ | ✓ | ~ | Open-source LLM engineering platform; tracing, eval, cost. |
| Helicone | ✓ | — | ✓ | — | ~ | — | LLM observability + caching + cost tracking. |
| Braintrust | ~ | ✓ | ~ | ✓ | — | — | Eval-first platform; prompt playground + regression detection. |
| Lunary | ✓ | ~ | ✓ | — | ✓ | — | Open-source LLM observability; tracing + cost. |
| OpenTelemetry GenAI | ~ | — | — | — | ✓ | ✓ | Semantic-conventions spec, not a product. Foundation other tools build on. |
This matrix is a capability checklist, not a benchmark. We do not publish performance, accuracy, or pricing scores unless we have collected and verified that data. Tool selection should follow your constraints, not a ranking.
How to decide
- Start from your risk. Is your primary failure mode quality regression (eval-first) or production debugging (tracing-first)? That single question eliminates half the field.
- Check your OTel investment. If you already run OpenTelemetry, an OTel-native tool (Phoenix) drops in with less instrumentation debt.
- Resolve data residency early. If you must self-host, the field narrows to Phoenix, Langfuse, and Lunary. Do not evaluate managed-only tools you cannot deploy.
- Separate eval from tracing if you must. A common mature pattern is OTel-compatible tracing plus a dedicated eval store. You do not have to buy one tool that does both.
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