LangSmith vs Arize vs Braintrust: Best LLM Tool 2026
Quick Comparison
| LangSmith | Arize Phoenix | Braintrust | |
|---|---|---|---|
| Best For | Teams building agents or LLM applications on LangChain or LangGraph who want observability and evaluation that's native to the framework rather than bolted on. | Teams running mixed traditional-ML and LLM workloads who want free, framework-agnostic, self-hosted observability with strong RAG evaluation. | Product teams whose core requirement is wiring evaluation results directly into a CI/CD pipeline, not just observing production traffic after the fact. |
| Pricing | Free tier available / custom pricing | Free tier available | Free tier available / $249/mo starting (Pro) |
| Winner | Our Pick |
Tool Breakdown
Arize Phoenix
Phoenix is the safest default for most teams — it's free to self-host indefinitely with no usage caps, works with any framework via OpenTelemetry, and its RAG-focused evaluators cover the most common LLM quality problem teams actually run into first.
- Free to self-host indefinitely with no usage caps — the only tool of the three with no tier to eventually outgrow
- OpenInference/OpenTelemetry-native instrumentation makes it vendor- and framework-agnostic, unlike LangSmith's LangChain-centric design
- Built-in LLM-graded evaluators purpose-built for RAG quality: retrieval relevance, hallucination detection, QA correctness
- Elastic License 2.0, not a fully permissive OSI license, restricts using Phoenix as the basis for a competing hosted service
- No native CI/CD gating workflow out of the box — teams wanting evals to block a deploy pipeline need to build that integration themselves or move to the separate managed Arize AX product
LangSmith
LangSmith is LangChain's own observability and evaluation platform, offering end-to-end tracing, prompt versioning, and test-suite integration that's most powerful when used with LangChain or LangGraph.
- Deepest tracing and debugging integration for LangChain/LangGraph-based agents of any tool in this comparison
- Unified dashboard for traces, datasets, and evaluation tests without standing up separate infrastructure
- Free tier available for evaluation before committing to a paid plan
- Advanced features are noticeably less capable for teams not using LangChain — framework-agnostic tracing works, but the deeper tooling assumes LangChain's abstractions
- Pricing beyond the free tier is custom, which makes it harder to budget for compared to Braintrust's flat Pro rate
Braintrust
Braintrust is an LLM observability and evaluation platform built around a trace-to-test pipeline, with open-source SDKs and an Apache-2.0 AI proxy, designed for teams that want eval results to actively gate CI/CD deploys.
- Generous free tier for evaluation work: 1M trace spans/mo, 1GB processed data, 10K scores, 14-day retention, no card required
- Trace-to-test pipeline is purpose-built to let failed evals block a deploy automatically — the most direct CI/CD-native workflow of the three
- Flat $249/mo Pro tier simplifies budgeting compared to LangSmith's custom pricing
- Core platform is proprietary — only the SDKs, the autoevals library, and the AI proxy are open source
- Full self-hosting is Enterprise-gated and requires contacting sales, unlike Phoenix's free self-hosting from day one
- No confirmed commission-based affiliate program
Frequently Asked Questions
Which LLM observability tool should I pick if I'm not using LangChain? +
Arize Phoenix or Braintrust — both are framework-agnostic, unlike LangSmith, whose deepest features assume a LangChain or LangGraph stack. Phoenix is the lower-risk starting point since it's free to self-host with no usage caps and instruments via the vendor-neutral OpenTelemetry standard. Braintrust is worth considering instead if your specific need is gating CI/CD deploys on eval results, since that workflow is more built-out in Braintrust than in Phoenix's core product.
Do I need to pay for any of these to get started? +
No — all three have a free tier. LangSmith and Braintrust offer free hosted tiers (Braintrust's is the more clearly documented: 1M trace spans/mo, 10K scores, 14-day retention). Arize Phoenix goes further: it's fully open source and free to self-host indefinitely with no usage caps at all, so there's no ceiling to eventually hit. Start with whichever tool matches your framework, then evaluate whether you need Braintrust's CI/CD-gating workflow or LangSmith's LangChain-native tracing enough to pay for a higher tier.
Can I use more than one of these tools together? +
Yes, and it's a common pattern in practice. A team might run Arize Phoenix during active development to evaluate RAG quality and debug retrieval traces at no cost, then move to LangSmith in production if they're deep in the LangChain ecosystem, or to Braintrust if they specifically need eval results to gate their deploy pipeline. Because Phoenix instruments via OpenTelemetry, its traces can flow into other OTel-compatible backends, so these tools cover adjacent stages of the LLM development lifecycle rather than being mutually exclusive.