The latest version of MediaWiki (version 1.22/wmf4) was added to non-Wikipedia wikis on May 13, and to the English Wikipedia (with a Wikidata software update) on May 20. It will be updated on all other Wikipedia sites on May 22. 
A software update will perhaps result in temporary issues with images. Please report any problems you notice. 
MediaWiki recognizes links in twelve new schemes. Users can now link to SSH, XMPP and Bitcoin directly from wikicode. 
The next version of MediaWiki (version 1.22/wmf5) will be added to Wikimedia sites starting on May 27. 
An updated version of Notifications, with new features and fewer bugs, will be added to the English Wikipedia on May 23. 
The final version of the "single user login" (which allows people to use the same username on different Wikimedia wikis) is moved to August 2013. The software will automatically rename some usernames.