"RUM" (Real User Monitoring) is the technical name for this specific Google Tag Manager tag — it isn't something you buy separately. It's the real-visitor data collection that powers your Monitoring subscription: confirms your CMP, GTM container, GA4, and Consent Mode are actually working for real visitors, on top of the synthetic checks Monitoring already runs.
CMP presence, GTM container load, GA4/ad-platform fire detection (by platform, not by request content), consent categories granted, and timing (CMP render, GTM load, consent-to-GA4 delay, time-to-consent-interaction). No IP address, no user agent, no user identifiers.
Looking for the server-side tracking tag instead? See sGTM beacon documentation.