Special:MediaSearch will be the default search experience on Commons starting 4/1 (for anonymous users) and 5/1 for all users (assuming no blockers arise). Logged in users will have the option to opt out via a preference and continue to use Special:Search as their default search experience (see T273979). We would like to measure what percentage of users choose to opt out and continue to use Special:Search as their default search experience. We'd like to see this number on a weekly basis.