4 Braintrust Alternatives That Bill Predictably (2026)

Braintrust is the best turnkey eval platform of the major tools. That is not the problem. The problem is the meter.

Braintrust bills on “processed data” in GB, and that number counts every byte - inputs, outputs, prompts, metadata, traces, spans, attachments, all of it. That is fine for a lean chatbot. It is a trap for a verbose multi-step agent or a RAG pipeline stuffing large contexts into every call. Those are exactly the apps you most want to trace, and they are exactly the ones that burn the GB allowance fastest.

Two things make it bite. The pricing goes from a $0 Starter tier straight to a $249/mo Pro tier with nothing in between. And above that there is no hard spending cap, so the $249 is a floor, not a ceiling. As Braintrust’s own product makes clear, the SDKs are open source but the Brainstore backend is closed, and self-hosting is hybrid-VPC and Enterprise-only - so you cannot just run it yourself to escape the meter.

So this is not a “Braintrust is bad” list. Its regression testing and CI/CD quality gates are genuinely the best in class. This is a list for the specific reason people leave it - the unpredictable bill on verbose workloads - and I have matched each alternative to why you are looking.

The short version

Tool	Best for	Billing model	Self-host	Starting price
Braintrust	Turnkey evals and CI quality gates	Processed data by the GB, no cap	Hybrid, Enterprise only	$249/mo
Langfuse	Open-source observability default	Billable units, or free self-host	Free, MIT, full product	$0 / $29/mo
Opik	Cheapest cloud, permissive OSS	Spans, or free self-host	Free, Apache-2.0, full product	$0 / $19/mo
DeepEval	Pytest-style evals in CI	Free OSS framework, or GB-month cloud	Free, Apache-2.0 framework	$0 / $200/mo
Arize Phoenix	OTel-native tracing and RAG eval	Free OSS, spans on managed cloud	Free, ELv2 server	$0

If you left because of the unpredictable bill: Langfuse

Langfuse is the open-source default in this category, and it fixes the exact thing that hurts on Braintrust. You can self-host the full product for free under MIT - only three features are enterprise-gated, and tracing, evals, prompt management and human annotation are all included. Self-host and the per-usage cost disappears entirely. No processed-data meter, no cliff, no surprise.

On the managed side it is cheap too. At 1M events a month, Langfuse runs about $101/mo. For comparable volume the closest closed platform runs many times that. The managed unit is “billable units” at $8 per 100k, which is far easier to forecast than bytes of processed data.

The honest catch is operational. Langfuse v3 needs Postgres plus ClickHouse, Redis and S3-compatible storage - four services to run - and the migration to that architecture is where self-hosters get stuck. The software is free. The ops time is not. If you have a team that can run a four-service stack, Langfuse is the cleanest escape from a usage meter you can’t predict.

If you left because of the price: Opik

If the whole reason you are leaving is cost, Opik is the shortest path. It is Comet’s open-source observability and eval platform, and it does two things Braintrust does not.

First, the open-source build is Apache-2.0 and genuinely complete - full feature set self-hosted, unlimited spans, members and retention, no gates. Second, if you want managed hosting, the Pro Cloud tier is $19/mo for 100k spans, the cheapest paid cloud of the major eval platforms. Against Braintrust’s $249 floor, that is an order of magnitude cheaper to start. It is also the fastest-growing project of its peers at roughly 20.8k GitHub stars, so the market is voting for it.

The catch is per-seat pricing at scale. Smaller startups report the cloud cost gets hard to justify as headcount rises, and a few large-project users mention occasional UI slowdown. Model the seat count before you commit the cloud. But for a small team that just wants predictable, cheap tracing and evals, Opik is the most honest deal here.

If you left because evals should live in your test suite: DeepEval

Braintrust’s pitch is that it hands you the eval orchestration. If you would rather own your evals as code in your own CI, DeepEval is the more natural fit. It is the closest thing to pytest for LLM apps - you write test cases, assert on metrics, and run deepeval test run in the pipeline. The open-source framework is Apache-2.0 and free forever, fully usable with no account, and it ships 50+ research-backed metrics including the widely-cited G-Eval.

This keeps your regression testing in version control and off a usage meter entirely. For the OSS framework there is no processed-data bill to blow up, because there is no bill.

Two honest gotchas. Nearly all of DeepEval’s metrics are LLM-as-judge, so a large suite fires a lot of inference calls - that compounds into API cost and slows runs to minutes, not seconds. And the Confident AI cloud, if you want the hosted UI, has its own steep cliff from $200/mo Starter to $2,000/mo Team. Live in the free framework as long as you can. If tests-as-code is your model, DeepEval is built for it.

If you want OTel-native tracing and the best RAG eval: Arize Phoenix

If your stack is standardizing on OpenTelemetry, Arize Phoenix is the most natural fit in the category. It is built on OpenTelemetry and Arize’s own OpenInference conventions, so it is vendor and framework agnostic. It runs locally in under a minute, ships 50+ pre-built eval metrics, and reviewers single out its RAG evaluation as the best available. The OSS build is free with no usage caps on the features themselves - no processed-data meter in sight.

The catch is the license, not the bill. The Phoenix server is Elastic License 2.0 - source-available, not OSI-approved open source - which forbids offering it as a hosted service to third parties. For internal use that restriction rarely comes up, and the product behaves like open source. Just know that “fully open source” overstates it, and that the separate Arize AX managed cloud has opaque pricing (the public page returned a 403 at our last check). For self-hosted OTel-native tracing plus deep RAG eval, Phoenix is the pick.

So which one?

• You need turnkey regression testing and CI quality gates, and you can watch the meter - honestly, stay on Braintrust and set billing alerts on day one. Nothing else is this complete for blocking bad merges out of the box. The alternatives exist for people the billing model does not fit, not because the product is weak.
• You want the full product, self-hosted and free - Langfuse if you have the ops capacity for a four-service stack, Opik if you want Apache-2.0 and a simpler run.
• You want the cheapest managed cloud - Opik at $19/mo, no contest.
• You want evals as code in your own CI - DeepEval, and live in the free framework.
• You are standardizing on OpenTelemetry and care about RAG eval - Arize Phoenix, license caveat noted.

One honest note. Braintrust’s processed-data model is not a scam - it is a real trade for a real product, and for lean workloads on a watched budget it is fine. The reason it lands people on this page is the combination of a verbose agent, the $0 to $249 cliff, and no spending cap. If that describes you, one of the four above will bill in a way you can actually forecast.