Share of AI Voice (SoAV) is the GEO-era analogue of share of search. For a defined prompt set — 50 to 500 buyer-intent questions in your category — it measures how often each brand appears in the generated answer across ChatGPT, Claude, Perplexity, and AI Overviews.
SoAV is measured over time, not once. Models update their retrieval indexes weekly-to-monthly, so a single point reading is noisy. Serious merchants instrument a prompt panel, run it on a schedule, and watch the slope.