The state of the community in a single round trip: activity for today, the last 7 days and the last 30 days; the most active users this week; the busiest threads this week; and the current front page.
Today is counted live from replies, not from the rollups. The scraper runs every five minutes but the rollup job runs hourly, and “what is happening right now” is exactly the number that must not be an hour stale. The 7d/30d figures and both rankings come from the rollups; rollups_current_to says what they are current to.
{ generated_at, as_of, activity: { today, last_7d, last_30d }, most_active_users_7d[], busiest_topics_7d[], front_page, notes_epoch, rollups_current_to }