Langfuse vs Braintrust 2026 - Open Self-Host vs Turnkey Evals

Langfuse and Braintrust get compared constantly, and the reason is that they are answering two different questions with overlapping products. Langfuse is the open-source observability default - cheap, self-hostable, framework-agnostic. Braintrust is the eval-first platform where regression testing and CI quality gates are the center of gravity. People pit them because both trace your app and both run evals, so on a feature checklist they look interchangeable. They are not. The right pick comes down to whether your priority is cheap open self-host or turnkey regression testing.

I have wired up both. Here is the honest split, and where Opik fits as a third option.

The short version

Axis	Langfuse	Braintrust
Best for	Cheap, open, self-hosted observability	Turnkey evals and CI regression gates
Starting price	Free / $29/mo	Free / $249/mo
Self-host	Free, MIT, near-complete	Hybrid VPC, Enterprise only, backend closed
License	MIT (OSI open source)	SDKs open, Brainstore backend closed
Billing unit	Billable units, $8/100k	Processed data by the GB, no hard cap
Cost at scale	~$101/mo at 1M events	Uncapped, punishes verbose agents

Where Langfuse wins: openness and cost

Langfuse is the default answer to “what is the self-hostable observability tool,” and it earns it. Self-hosting is free under MIT, and only three features are enterprise-gated - tracing, evals, prompt management, human annotation and RBAC are all included. You run the real product on your own infrastructure, data never leaving your cloud. On the numbers it runs about $101/mo at 1M events managed, and self-host removes the per-trace cost entirely. It is framework-agnostic and maps the OpenTelemetry GenAI semantic conventions.

The catch is operational, not commercial. Langfuse v3 moved to Postgres plus ClickHouse, Redis and S3-compatible storage - four services - and the migration to that architecture is where self-hosters get stuck, with GitHub threads reporting memory errors and timeouts. It is also a ClickHouse subsidiary now after the January 2026 acquisition, worth weighing on a multi-year bet. And for full regression testing, you assemble more of the orchestration yourself - which is exactly where Braintrust pulls ahead.

Where Braintrust wins: turnkey regression testing

Braintrust started with evals and built observability around them, and it shows. The autoevals library ships working scorers out of the box - exact match, embedding similarity, LLM-as-judge factuality - and the CI/CD quality gates can block a merge on a statistically significant regression, not just log that quality dropped. Human review, automated scorers, tracing and datasets all share one system. There is no per-seat charge, users are unlimited on every tier, and it is well-backed after an $80M Series B led by Iconiq in February 2026 at a roughly $800M valuation. If your core question is “did this change make the model worse, and can I block the merge if it did,” this is the platform built for it.

The gotcha is the billing meter. Braintrust bills “processed data” in GB, counting every byte of inputs, outputs, prompts and metadata, and there is no hard spending cap. The $0 Starter jumps straight to $249/mo with nothing in between. Verbose multi-step agents and big RAG contexts - the workloads that most need observability - burn the allowance fastest. And self-host is hybrid-only and Enterprise-only, with the Brainstore backend closed, so you never fully own the stack. Set up billing alerts on day one, or the $249 plan will not stay $249.

Langfuse vs Braintrust: which should you pick?

• You want cheap, open, self-hosted observability and can run the stack - Langfuse. Nothing else gives you this much for free, and the cost gap at scale is enormous.
• Regression testing and blocking bad merges is the whole point - Braintrust, with billing alerts on from day one. The autoevals-plus-CI-gates combo is more turnkey than assembling it on Langfuse.
• You are compliance-sensitive and need data residency - both can keep data in your cloud, but differently. Langfuse via a free MIT self-host you fully own; Braintrust via an Enterprise hybrid VPC where the backend stays closed. If you want to truly own the stack, Langfuse.
• You run verbose agents or large RAG contexts on a tight budget - lean Langfuse. Braintrust’s per-byte meter punishes exactly those workloads.
• You are on LangChain and want tighter eval-judge calibration - neither is the obvious answer; that is more LangSmith’s Align Evals territory. Between these two, Braintrust for eval depth.

Where Opik fits

If neither extreme fits, Opik is the middle path. It is Comet’s open-source platform, Apache-2.0 with the full feature set self-hosted and no gates - more permissive than anything here - and its Pro cloud is $19/mo for 100k spans, the cheapest paid cloud of the major platforms. It does evals too - LLM-as-judge, code metrics, online evaluation, guardrails and an Agent Optimizer. It gives you Langfuse-style openness with a simpler self-host story and a cheaper managed tier, though its eval workflow is not as turnkey for CI regression gates as Braintrust’s. The honest watch-out is per-seat pricing at scale - model it if you are a big team.

Bottom line

Langfuse if openness and cost decide it; Braintrust if turnkey regression testing does. Langfuse is the cheaper, more open, more self-hostable default, and for most teams tracing production LLM apps it is the safer starting point. Braintrust is the one to pick when blocking bad merges on measured regressions is the job you came for, provided you watch the uncapped meter. And if you want a permissive-license middle ground with the cheapest cloud, look hard at Opik. Every price and date here is from each vendor’s public pages, verified on 26 July 2026. This category ships breaking changes monthly - we re-verify every 30 days.