# What is a hallucination rate?

> A hallucination rate is the share of a model's answers that are confidently wrong, measured against real questions with known correct answers.

Source: https://meshin.co/glossary/hallucination-rate
Updated: 2026-10-02

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## Why it comes up

A board asks this before it asks about model architecture or vendor choice. It turns "is the AI any good" into a number anyone can track quarter to quarter. A company that cannot answer with one, measured on its own real use cases, is really saying "we do not know." That reads differently in a board pack than an honest figure with the method stated plainly.

## What to do about it

Measure the rate on the eval suite's real cases, not a generic public benchmark. Behaviour on general trivia says little about a specific product's actual questions. Track the number after every prompt or model change, the way a team tracks an eval pass rate. Do not measure it once and assume it holds. The [90-Day Production Sprint](/services/90-day-production-sprint) puts this measurement inside continuous integration, so a regression blocks a release.