Arize Phoenix vs Braintrust
Detailed side-by-side comparison to help you choose the right tool
Arize Phoenix
🔴DeveloperAI Observability
Phoenix is Arize's open-source LLM observability project, and it has quietly become the default way tens of thousands of teams see what their agents are actually doing in production. The pitch is simple: `pip install arize-phoenix`, instrument with OpenInference (or any OpenTelemetry-compatible library), and every LLM call, tool invocation, retrieval, and embedding shows up as a spanned timeline you can filter, search, and replay. No vendor account required, no proprietary SDK lock-in. The Open
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Starting Price
FreeBraintrust
🔴DeveloperLLM Observability
AI observability platform for evals, production tracing, prompt management, and regression detection.
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Starting Price
FreeFeature Comparison
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💡 Our Take
Choose Braintrust if you want a managed SaaS platform with automated prompt optimization and a polished evaluation workflow — minimal setup and the Loop agent are the wins. Choose Arize Phoenix if you need open-source ML observability with deep support for embeddings, RAG debugging, and on-prem deployment for compliance reasons. Phoenix is stronger for ML researchers and RAG-heavy applications; Braintrust is better for product teams shipping LLM features fast.
Arize Phoenix - Pros & Cons
Pros
- ✓Permissively open source — full features without a vendor account
- ✓OpenTelemetry-native means Phoenix traces also flow into Datadog, Honeycomb, Tempo
- ✓Local dev loop is 30 seconds: install, instrument, see traces
- ✓Auto-instrumentation covers virtually every major LLM and agent framework
- ✓Upgrade path to managed Arize Cloud or enterprise AX without re-instrumenting
Cons
- ✗UI prioritizes function over polish — LangSmith and Langfuse have nicer dashboards
- ✗Advanced alerting, drift detection, and RBAC sit in paid Arize AX, not open core
- ✗Production self-hosting still requires you to operate PostgreSQL and storage
- ✗Evaluation primitives are powerful but require Python — no no-code eval builder
- ✗Documentation occasionally trails the rapid OpenInference instrumentation pace
Braintrust - Pros & Cons
Pros
- ✓Evals, tracing, and prompt playground in a single shared workbench
- ✓Playground pulls real production traces in for side-by-side comparison
- ✓Regression detection across model swaps is a first-class workflow
- ✓Native integrations with the major SDKs (OpenAI, Anthropic, LangChain, Vercel AI)
- ✓MCP support makes tool traces structured spans rather than blobs
Cons
- ✗Jump from Free to $249/mo Pro is steep with limited middle tier
- ✗LLM-as-judge scorers require careful rubric design to be reliable
- ✗Opinionated workflow — friction if your team prefers fully custom pipelines
- ✗Self-host only on Enterprise
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