See {T183869} and [[https://meta.wikimedia.org/wiki/Research:Spambot_detection_via_registration_page_behavior|m:Research:Spambot detection via registration page behavior]] for context, and {T183991} for the UI. Plan is to deploy to group1 on Monday and group2 on Tuesday. The first step involves backporting #mediawiki-extensions-wikimediaevents and #mediawiki-extensions-campaigns patches to the active WMF branch; the second is just a config change.
Adding #performance-team for visibility. The patch pulls in OOUI core for the popup widget, which adds ~50K (after gzip) Javascript to the registration page, which means almost doubling the size of the page. (This is done on desktop only.) Assuming this is not a big deal since it has to be done sooner or later anyway due to T85853.
Monitoring is tracked in T185870. The logging code is planned to be live for about a month.