If you can't tell whether your AI feature got better or worse this week, you don't have an AI feature — you have a vibe.
We start every AI engagement by writing the eval set before the prompt. 100–300 cases drawn from real user questions, scored by a reference model and spot-checked by a human.
Once you have evals, everything downstream gets easier. Model swaps become a regression test. Prompt edits ship behind a flag with confidence intervals. Cost optimisation stops being a guess.
The team that owns the eval set owns the AI feature. Make sure that's your team, not your vendor's.