I've just deployed the ApiFeatureUsage extension to Beta Labs for testing.
If an API client (e.g. a bot or a user script) sets a unique User-Agent or
Api-User-Agent header, a summary of deprecated API features hit by that
client may be fetched from Special:ApiFeatureUsage or from the API
Please try it out, and report any issues in Phabricator using the
MediaWiki-extension-ApiFeatureUsage project. If things look good after
testing I'll be looking at getting it deployed to production in the next
month or so.
Brad Jorsch (Anomie)