Braintrust CEO: Evals Are the Modern PRD — Build the Feedback Loop First
Summary
Ankur Goyal (Braintrust CEO) lays out a concrete eval-driven product process: treat evals as the modern PRD, build a feedback loop that turns real production data into new evals continuously, and run 4–6 agents simultaneously rather than sequential refinement. Key principles: 'practical quality beats theoretical quality'; when agents fail, improve the eval rather than the prompt; encode domain expertise (including designer taste) in scoring functions, not just functional correctness. Braintrust positions evals as the mechanism for turning AI usage signals into product decisions.
Why this signal
Directly maps to Neo's #2 focus area ('eval is the new PRD'). Goyal is a named practitioner with a real company and gives actionable structural guidance — not just philosophy. The 'encode designer taste in scoring functions' point is novel and applicable to Thomas Engineering's cross-functional AI adoption work.
Original email
Lenny's Newsletter · 6/15/2026
🎙️ How I AI: Claude Fable 5 review & How Braintrust uses AI agents, evals, and CI to ship better software