Counts visible talent only by default (isHidden is not true and archivedAt is null). Pass onlyReturnHiddenTalent=true to count only hidden talent instead, or includeHidden=true to count BOTH visible and hidden talent (archived still excluded). For Match Score counts, vectors[matchUuid] takes the Pool entity's own uuid (for matchType Opening, a Hire funnel id is also resolved via the opening's hireExternalId); an identifier found in neither space is rejected as a 400 naming the unresolvable id. averageScore is DEPRECATED here and returns null unless the query carries vectors — use GET /talents/averageScore instead. It stays in this response for one release so existing consumers keep parsing.