Cost vs Braintrust: an honest comparison

Braintrust is a far more complete answer to the quality question, and quality is the question most teams have first. If you need to build an eval suite, run experiments across prompt versions, score outputs with graders you write yourself, and let a non-engineer iterate in a playground, Braintrust does all of that properly and Cost does none of it.

Its deployment story is also stronger than ours for a regulated buyer. Self-hosting and bring your own cloud are both supported on AWS, GCP and Azure, with experiment records, logs, traces and datasets staying in your own data plane while Braintrust keeps only project names, settings, hashed keys and auth. If your security review requires that shape, Braintrust has it documented and we do not offer an equivalent.

Unlimited users on every tier is a real advantage for a team that wants everyone looking at the same evals. And the free Starter tier is genuinely usable for a small project rather than a demo.

The meters point in opposite directions. Braintrust charges for processed data and for scores, so the more of your system you watch, the more you pay to watch it. That is the right shape for an eval platform you point at the routes that matter, and the wrong shape for spend visibility, which is only useful when it covers everything. Cost charges against a band of your model spend, so turning it on for one more route costs nothing.

Cost answers a question Braintrust does not ask. Not whether this output is good, but which route is burning the money and whether the cheaper model would have been fine. The verification step is the product: the cheaper model runs against real traffic, an independent judge scores the answers across five dimensions, and the recommendation only appears when it matches. You apply the change yourself.

Fourteen day retention on the free tier and thirty on Pro is short for cost work. A spend argument is usually about a trend over months, and the question that starts it is almost always about last quarter.

If you are an engineering lead whose AI feature is shipping but whose bill has doubled since March, Cost is the one that answers your question. You need the spend split by route, and you need evidence that moving the expensive route down a tier will not break it. That is the entire product.

If you are a team arguing about whether the new prompt is better than the old one, Braintrust is the right tool and nothing in Cost will help you. Buy the eval platform.

If you are both, which is common, the honest answer is that they are complementary rather than competing, and the order matters. Measure the spend first, because it tells you which route is worth the eval effort. There is no point building a careful eval suite for a route that costs eleven euro a month.

If your security review requires that no prompt or response body leaves your infrastructure, both can satisfy it, but by different routes. Braintrust wants an Enterprise contract and a deployment you run. Cost keeps bodies in your network by default on every tier, because the SDK only sends cost metadata unless you opt a route in.

Yes, and the combination is coherent. Braintrust scores whether the output is right. Cost tells you what the output costs and whether a cheaper model produces an answer that still passes. They both wrap the same client calls and neither sits in the request path, so running both is an engineering decision rather than an architectural one.

The sequence we would suggest is Cost first for a fortnight, because it is cheap to turn on and it tells you which three routes actually matter. Then put the eval effort into those three.