R Rex

AI-native service running accounts receivable and order-to-cash for finance teams.

Rex instrumented its agents in Braintrust from its first enterprise customer, tracing every touchpoint before it had enough domain data to write good evals. Those traces became the eval bank, which in turn made model selection routine — cheaper, faster models go wherever measurement says they hold up. User corrections on agent drafts are captured as custom facets and grouped continuously, and negative feedback automatically kicks off an overnight coding-agent investigation against the same instrumentation.

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