Eval-Driven Product Management: How to Define "Good" for AI Features
Shipping AI features without evals is how 95% of pilots fail. Here is how product managers define "good" for probabilistic features — and ship with evidence instead of hope.
Most teams ship AI features the way they ship buttons: write a spec, build it, click around once, call it done. Then it hallucinates in front of a customer. The problem isn't the model — it's that nobody defined what "good" actually means before shipping. That's the job of an eval, and writing them is fast becoming the core product-management skill of 2026.
The PRD Tells You What to Build. Evals Tell You If It Works.
For a deterministic feature, "done" is obvious: the button saves the form or it doesn't. For a probabilistic feature — a summarizer, an agent, a RAG-powered answer — "done" is a distribution. The same prompt can produce a brilliant answer on Monday and a confidently wrong one on Tuesday. A PRD that says "summarize the customer call" is meaningless without a definition of what a good summary contains, what a bad one looks like, and how often you can tolerate the bad one.
An eval is that definition made executable: a set of test cases, each with an input and a rubric for grading the output. It is the user story for a system that never behaves the same way twice.
Why This Lands on the PM, Not the ML Engineer
MIT's widely-cited 2026 finding that 95% of enterprise GenAI pilots deliver no measurable ROI is not a modeling failure — it is a product-judgment failure. An engineer can make a model score higher on a benchmark. Only the PM knows which failures actually cost you a customer. Deciding that a refund bot must never invent a policy, but may occasionally ask a clarifying question, is a product call, not an engineering one. Evals are where that judgment gets written down.
How to Write Your First Eval Set
- Collect real inputs. Pull 20–50 actual examples — support tickets, call transcripts, user queries. Synthetic cases miss the messiness that breaks models in production.
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