Business Pill 20 · Good enough, defined in advance
You cannot inspect every answer an AI gives. You can define in advance what passing means. That written-down definition is the evaluation.
A short explainer video. The numbers in it are round numbers for illustration.
Why a Single Test Is Not Enough
With ordinary software this was simple. You wrote a test. The same input always gave the same output, so the test passed or it failed.
AI does not behave that way. Ask the same question three times and you may get three different answers. Two may be fine. One may be subtly wrong. A single test tells you very little.
Measuring It Differently
So you measure it differently. You collect a set of real examples where you already know what a good answer looks like. You run the system on all of them, and you count how often it gets it right.
Think of a driving test. Nobody can watch a driver on every road for the rest of their life, so we define a set of situations and a passing score. Pass, and you get the licence.
A Worked Example
The video uses round numbers. You gather 200 real cases and set the bar at 95%. Version one scores 90%. It does not ship.
Used this way, the evaluation becomes the acceptance test. It is the definition of good enough, written down in advance.

Why It Matters
This matters more than it seems. Whoever writes the evaluation decides what good means. And every time the model changes, you run it again, so a change that breaks something gets caught before your customers see it.
Three Questions to Ask
- What are our real cases?
- What score is good enough?
- Who decides?
See It in the News
Anthropic’s Claude Opus 5.5 System Card: What the Numbers Actually Measure. A news piece on reading what an evaluation figure does and does not measure.
How This Concept Connects
Layer 2 of 8 · Models & Training, on the Business Engineer Concept Map
- Benchmarks contrasts with AI Evaluation as Acceptance Test. A benchmark’s public questions are not yours; an acceptance evaluation uses your own real cases and a bar set in advance.
- Discardable Software builds on AI Evaluation as Acceptance Test. The checks that tell you the program did the right thing must last even when the code is thrown away.
- The Residency Model builds on AI Evaluation as Acceptance Test. The residency’s last step is a test on the work itself, judged on real cases like an acceptance test.
- Outcome-Based Pricing builds on AI Evaluation as Acceptance Test. Both sides must agree in advance what counts as solved and who measures it, as in an acceptance test.
- AI Evaluation as Acceptance Test builds on Overfitting. An evaluation counts on real cases with known answers, following the overfitting rule to test on what the model has not seen.
- Model Deprecation (lesson unlocks soon) builds on AI Evaluation as Acceptance Test. The defense against deprecation is keeping your own test cases and rerunning them before every switch, an acceptance evaluation.
- AI Evaluation as Acceptance Test contrasts with Post-Market Surveillance (lesson unlocks soon). An acceptance test decides before shipping; post-market surveillance keeps checking in real use because a test shows one day.
- AI Evaluation as Acceptance Test builds on Panel Data (lesson unlocks soon). An evaluation set of real examples stands in for all real use, so who is in that sample shapes the score.
Pragmatic Rigor vs Precision Theater
Defining ‘good enough’ in advance is pragmatic rigor.
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