Langfuse and Phoenix are open source and self-hostable (Phoenix with no feature limits); LangSmith comes from LangChain and adds agent deployment; Braintrust is a hosted eval-first platform with self-hosting on Enterprise. All four accept OpenTelemetry traces. They are for teams moving agents to production who need to debug runs, run experiments and watch quality and cost.
*Field guide compiled 2026-10-23 from the official documentation, pricing pages and changelogs linked below; every line links to the page that states it.*
What it does
- LLM Application & Agent Tracing. Langfuse records traces and agent graphs, sessions (chats/threads), users, and token and cost usage. How: Langfuse Python or JS/TS SDK, native framework integrations, OpenTelemetry, or LiteLLM proxy logging source
- OpenTelemetry (OTEL) for LLM Observability. Send OTEL traces from any application, framework or collector to Langfuse; Langfuse recommends its SDK for Python and JS/TS. How: Configure an OTLP exporter to Langfuse per the OpenTelemetry integration page source
- Evaluation (online and offline). Langfuse datasets, experiments via SDK and UI, custom scores, user feedback, LLM-as-judge evaluators and human annotation queues. How: Langfuse Evaluation features; Hobby includes 1 annotation queue source
- LangSmith Observability & Evaluation. Tracing, monitoring, insights, online and offline evals, dataset collection, annotation queues, Prompt Hub and Playground, bulk export. How: LangSmith SDK or integrations for LangChain, LangGraph, OpenAI Agents SDK, Claude Agent SDK, CrewAI and others source
- Trace with OpenTelemetry. LangSmith ingests OTel traces from LangChain and non-LangChain apps and maps GenAI standard, TraceLoop, OpenInference and Logfire attributes. How: Configure OTLP endpoint and environment variables per the LangSmith OpenTelemetry guide source
- LangSmith Deployment. Deploy and manage long-running agents, expose an agent as an MCP server, stream intermediate steps, scale to zero when idle. How: Plus plan includes 1 free Serverless (Small) deployment source
- Send OpenTelemetry traces and logs to Braintrust. Braintrust accepts traces and logs through an OTLP trace exporter or a Braintrust span processor. How: Point an OTLP exporter at Braintrust or add the Braintrust span processor source
- Loop agent. Braintrust's built-in AI agent that runs evaluations, generates test cases and iterates on prompts. How: Available in the Braintrust platform source
- Tracing in Phoenix. Phoenix accepts traces over OpenTelemetry (OTLP) and auto-instruments LlamaIndex, LangChain, DSPy, Mastra, Vercel AI SDK, OpenAI, Bedrock, Anthropic in Python, TypeScript and Java via OpenInference. How: Install OpenInference instrumentation and export OTLP to a Phoenix instance source
- Evals in the Phoenix UI. Score traces and spans with LLM-based evaluators, code checks or human labels; bring evaluators from Ragas, Deepeval or Cleanlab. How: Phoenix evals, dataset evaluators and human annotations in the UI source
Modes
- Langfuse Cloud. Fully managed by the Langfuse team; data region US, EU or JP. source
- Docker Compose. Langfuse self-hosting for local use and testing on a single VM without high availability, scaling or backups. source
- Kubernetes (Helm). Langfuse production self-hosting (also AWS, Azure, GCP); depends on PostgreSQL, Redis/Valkey, ClickHouse and S3/blob storage. source
- Phoenix self-hosting. Free to self-host with no feature limitations, can be fully air-gapped; Docker, Kubernetes, Cloud Run and others. source
- LangSmith Enterprise. Self-hosted and hybrid deployment options with custom SSO, ABAC and RBAC. source
- Braintrust Enterprise. On-prem or hosted deployment for high-volume or privacy-sensitive data. source
Pricing and limits
- Langfuse Core: $29 / month. 100k units / month included, additional $8/100k units, 90 days data access, unlimited users source
- Langfuse Pro: $199 / month. 100k units included then $8/100k, 3 years data access, high rate limits; Teams add-on $300/mo source
- Langfuse Enterprise: $2499 / month. Audit logs, SCIM API, custom rate limits, uptime and support SLA source
- LangSmith Developer: $0 / seat per month then pay as you go. Up to 5k base traces / mo, 1 seat source
- LangSmith Plus: $39 / seat per month then pay as you go. Up to 10k base traces / mo, unlimited seats, 1 free Serverless (Small) deployment; usage metered at $1.00 / LSU source
- Braintrust Starter: $0 / month. $10 credits, 1 GB processed data + $4/GB, 10k scores + $2.50/1k, 14-day retention, unlimited users source
- Braintrust Pro: $249 / month. $100 credits, 5 GB processed data + $3/GB, 50k scores + $1.50/1k, 30-day retention + $0.50/GB/mo source
- Arize AX Pro: $50 per month. 50k spans per month, 10 GB ingestion, 30 days retention source
Recent changes
- 2026-10-22: Langfuse self-hosted Enterprise can run in FIPS mode on FIPS 140-3 validated modules; images rebuilt on Iron Bank hardened Red Hat UBI 9. source
- 2026-10-21: Langfuse can export score metadata and provenance to S3, GCS and Azure scheduled exports. source
- 2026-10-18: Langfuse experiments chart every score across runs and compare candidates item by item against a baseline. source
- 2026-10-15: Langfuse project API keys can be created with limited permissions. source
Alternatives
- Arize AX. Arize's managed enterprise platform built on the same open standards as Phoenix, with paid tiers from $50 per month and self-hosting only on Enterprise. source
Traps
- Langfuse self-hosting with Docker Compose has no high availability, scaling or backups; production needs Kubernetes or a cloud deployment with PostgreSQL, ClickHouse, Redis and blob storage. source
- Some Langfuse self-hosted add-on features require a license key. source
- Langfuse Hobby API rate limits are low: 30 requests/min general API and 100 requests/day for Metrics API v2. source
- LangSmith free Developer plan is limited to 1 seat and 5k base traces per month before pay-as-you-go. source
- Braintrust Starter keeps data only 14 days and allows 1 human review score per project. source