Braintrust Alternatives

Langfuse is the tool most often named as the direct replacement for Braintrust. It started from tracing rather than evaluation: every call to a model becomes a trace with its prompt, answer, tokens, cost and latency, and agent steps nest inside it. On top it adds datasets, experiments, scores from model judges or humans, annotation queues, prompt versions and dashboards, so the Braintrust eval loop maps onto it without a gap. It accepts OpenTelemetry data, so most frameworks send traces without a dedicated SDK. The core is under the MIT license, only the ee folders carry a commercial license, and ClickHouse, which bought Langfuse in 2026, announced no planned licensing change.

Pricing is per unit, and a unit is any data point: a trace, each observation inside it and each score. Hobby is free with 50,000 units a month, 30 days of data access and 2 users. Core costs $29 a month with 100,000 units, 90 days and unlimited users, then $8 per 100,000 units. Pro costs $199 a month with 3 years of data access. A month of 10,000 agent runs with 30 steps and 3 scores each is 340,000 units, so $48.20 on Core, against $249 for Braintrust Pro. Self-hosting is free but heavy: Postgres, ClickHouse, Redis and object storage to run yourself.

Phoenix is the open-source tracing and evaluation tool from Arize. It is built on OpenTelemetry and the OpenInference conventions, so the same instrumentation captures LangChain, LlamaIndex, the OpenAI SDK, DSPy or your own code. You get the span tree of each request, evaluations with model judges on spans or whole traces, datasets, experiments that compare prompt versions on the same examples, and a prompt playground. For a Braintrust user, the appeal is simple: Arize states that self-hosted Phoenix has no license fees, no usage limits and no feature gates, and it ships as a Docker image, with Compose, or on Kubernetes with a Helm chart.

Read the license before you call it open source in a legal review: Phoenix is under the Elastic License 2.0, which lets you use and self-host it freely but not resell it as a managed service. When you do not want to run it, Arize sells a managed product, AX. AX Free gives 25,000 spans and 1 GB of ingestion a month. AX Pro costs $50 a month for 50,000 spans and 10 GB. Spans are steps, not scores, so a 30-step agent run uses 30 of them: AX Pro covers about 1,666 such runs a month, a light load next to Braintrust Pro, but at a fifth of the price.

LangSmith is the observability and evaluation platform of the LangChain team, and the polished managed product closest to Braintrust in how it feels. With LangChain or LangGraph you turn tracing on with environment variables and every chain, tool call and agent step appears as a nested trace. It also accepts other frameworks and plain SDK calls. Around tracing you get datasets, offline and online evaluations, annotation queues for human reviewers, a prompt hub and dashboards. Our LangChain review covers the framework, and the LangChain alternatives page helps if you are unsure you will keep it.

The price model is the opposite of Braintrust's. Braintrust gives unlimited users and bills data and scores; LangSmith bills seats plus traces. Developer is free for 1 seat with 5,000 base traces a month. Plus costs $39 per seat a month and includes 10,000 traces in total, then 0.005 LSU per extra trace, with one LSU at $1, so half a cent. Five engineers pay $195 a month before any extra trace, still below Braintrust Pro, but ten seats cost $390. Base traces are kept 14 days and extended traces 180 days at a higher rate. Startups backed by venture capital can get up to $10,000 in credits.

Opik is the LLM evaluation and tracing tool from Comet, the company known for machine learning experiment tracking. It covers the Braintrust workflow end to end: traces and spans, datasets, experiments, model-judge metrics, online evaluation rules on production traffic and prompt versions, plus guardrails and an agent optimizer that tries prompt variants for you. Integrations cover OpenAI, Anthropic, LangChain, LlamaIndex, CrewAI, DSPy and OpenTelemetry. The code is under the Apache 2.0 license, a true open-source license, and the self-hosted edition has unlimited spans and retention.

The cloud is the cheapest we found. Free Cloud gives 25,000 spans a month for up to 10 team members. Pro Cloud costs $19 a month for up to 50 members, 100,000 spans and 60 days of retention, then $5 per 100,000 extra spans; longer retention costs $29 per 100,000 spans. A month of 10,000 agent runs with 30 steps is 300,000 spans, so $29 on Pro Cloud, and one million spans comes to $64. That is a fraction of Braintrust Pro at $249, with twice its default retention. The catch: Opik counts spans, so very chatty agents use the quota quickly, and self-hosting runs on ClickHouse, MySQL and Redis.

Confident AI is the cloud platform built on DeepEval, an open-source evaluation framework under the Apache 2.0 license that many teams already run in pytest. DeepEval ships ready-made metrics, including a RAG set that scores the retriever (contextual relevancy, precision and recall) and the generator (answer relevancy and faithfulness), plus agent and conversation metrics and custom judges. The cloud adds tracing, datasets, regression reports between runs, online evaluations on production traffic, and red teaming and governance modules on higher plans. If your Braintrust use is mostly scorers in CI, this is the closest swap: the metrics run in your code and the results land in a shared dashboard.

Pricing is per organization. Free includes 1 GB of trace spans with one week of retention and 5,000 online eval runs a month; extra spans are dropped, not billed. Starter costs $200 a month with unlimited seats, up to 5 projects and 5 GB-months of spans, then $1 per GB-month ingested or retained, and 50,000 online eval runs. Team jumps to $2,000 a month. Starter sits $49 below Braintrust Pro, but the next step, Team, costs ten times Starter. Startups that raised less than $5 million can apply for a grant.

Weave is the LLM part of Weights & Biases, now sold under the CoreWeave Forge plans. You decorate your functions, or use one of its integrations, and each call is logged with inputs, outputs, cost and latency in a trace tree. Evaluations run a model or prompt on a dataset with scorers, and leaderboards line up the results, close to how Braintrust experiments compare runs. The SDK is under the Apache 2.0 license. Its edge is context: if your team fine-tunes models or logs training experiments in W&B, the LLM traces sit next to those runs, with the same projects, permissions and reports, and one vendor to review instead of two.

Like Braintrust, Weave bills data size rather than traces. The free plan includes 1 GB of Weave data ingestion and 5 GB of storage a month. Pro starts at $60 a month, billed monthly, with 1.5 GB of Weave ingestion and 100 GB of storage, and volume discounts on annual commitments. That is about a quarter of Braintrust Pro, but with less than a third of its 5 GB of processed data, so a verbose agent can push you past the quota fast. Outside the W&B ecosystem, the bundle brings little that Langfuse or Phoenix do not.