Hello,
After several months of hard work by the Discovery Search https://www.mediawiki.org/wiki/Wikimedia_Discovery/Search team, we're happy to announce that the CirrusSearch https://www.mediawiki.org/wiki/Extension:CirrusSearch backend has been upgraded to ElasticSearch https://www.elastic.co/products/elasticsearch version 5. This update was bit tedious and difficult for the team; you can browse the various tickets https://phabricator.wikimedia.org/T154501 in Phabricator if you'd like to know more.
This upgrade to ES5 is great, because we now have a new Ukrainian analyzer to experiment with, a new reindexing API and soon, we’ll have an updated completion suggester - all of which makes our backend more standard and reduced a significant amount of technical debt.
Cheers from the Discovery Search Team!
-- deb tankersley irc: debt Product Manager, Discovery Wikimedia Foundation