Because answer engines return prose instead of ranked lists, classic rank tracking doesn't apply. Citation share replaces it: define a panel of prompts your customers actually ask, run them on a schedule across ChatGPT, Perplexity, and Gemini, and record which domains get cited. Your share of those citations — and its trend — is the KPI.
Citation share responds to the same inputs as AI visibility: crawler access, extractable content, schema, and authority. It typically lags fixes by weeks, since engines refresh their retrieval indexes on their own cadence.