# How Rex uses Braintrust

**30-min**: “Continuous signal, 30-min fix cycles”

As published on [braintrust.dev](https://www.braintrust.dev/customers/rex). Captured by usedby on 2026-10-06.

- Company: [Rex](https://www.usedby.ai/companies/rex.md)
- Tool: [Braintrust](https://www.usedby.ai/tools/braintrust.md)

## What the story says

Rex, an AI-native accounts receivable and order-to-cash service, uses Braintrust to trace every agent touchpoint, run evals that let it swap models with confidence, and surface quality issues continuously through Topics and custom facets. Negative customer feedback also triggers coding agents that investigate overnight using Braintrust traces.

Summary written by usedby from the source page, in English. The figures are those of Braintrust and Rex, not ours.

> The next time we're online we've already got a ready-made investigation that's looked at the prompts, come up with a suggestion for how it would fix it, looked at the Braintrust traces. Then we can just go ahead and merge that PR.

> The biggest value prop of evals for us is being able to swap a different model in and out with confidence, either different models from the same provider or models from different providers, without the risk that outcomes are suddenly going to change.
>
> Lewis Blackwood, Co-founder

## What usedby checked

We compared the story with its live page on 2026-10-06.

- Checked: the figure 30-min is printed word for word on the page, near the name of Rex.
- Checked: the passage quoted above is copied word for word from the page, near the name of Rex.
- Checked: Rex uses Braintrust. Confirmed line. Latest check across sources: 2026-10-06.
- Not checked: the result itself. We quote it; we did not measure it.

---
Source: https://www.usedby.ai/case-studies/rex-braintrust · How we check: https://www.usedby.ai/methodology