Asymmetric Eval Economics: Why One Eval Case Costs More Than the Feature It Tests
Here is the awkward truth most AI teams discover six months too late: a single well-designed eval case routinely costs more engineering effort than the feature it is supposed to test. A prompt edit takes an afternoon. The eval case that gives you confidence the prompt edit didn't break something takes a domain expert two days of labeling, a calibration loop with a judge prompt, and a discussion about what "correct" even means for this user surface. The feature ships in a sprint. The eval that lets you ship the next ten features safely takes a quarter to mature.
The asymmetry isn't a bug. It is the structural shape of evaluation work. Labeling, edge-case curation, judge calibration, and rubric design are upfront fixed costs that don't scale with how many features you ship — they scale with how many distinct behaviors you want to verify. Meanwhile the feature side keeps producing what feels like cheap marginal output: "another prompt iteration," "one more tool added to the agent," "swap the model." Each looks individually small. Each silently increases the surface area the eval set must cover.
