An initial read is sized to a minimum of 100 observations per reported cell, per platform, per market. At a rate near 50%, that places the 95% range at roughly ten points at the worst case, and considerably tighter for rates further from the middle. It is enough to establish a defensible headline rate and a variance floor that later readings can be measured against.
A cell is the level at which a number is reported. Presence on ChatGPT in the United States in English is one cell. The same brand on Claude in France in French is another. We do not pool cells to reach a sample size, because pooling is what produces a global average that hides the variation you need to decide on.
Where a decision requires a tighter answer, for example establishing that a change between two reads is real, the sample is sized up for that specific comparison. We say in the report which figures are sized for a headline read and which are sized to support a comparison.