At Wikipedias, all new accounts now get the Growth features by default when creating an account. Communities are encouraged to update their help resources. Previously, only 80% of new accounts would get the Growth features. A few Wikipedias remain unaffected by this change.
You can now prevent specific images that are used in a page from appearing in other locations, such as within PagePreviews or Search results. This is done with the markup class=notpageimage. For example, [[File:Example.png|class=notpageimage]].
There has been a change to the HTML of Special:Contributions, Special:MergeHistory, and History pages, to support the grouping of changes by date in the mobile skin. While unlikely, this may affect gadgets and user scripts. A list of all the HTML changes is on Phabricator.
The new version of MediaWiki will be on test wikis and MediaWiki.org from 22 February. It will be on non-Wikipedia wikis and some Wikipedias from 23 February. It will be on all wikis from 24 February (calendar).
The software to play videos and audio files on pages will change soon on all wikis. The old player will be removed. Some audio players will become wider after this change. The new player has been a beta feature for over four years.
Toolforge's underlying operating system is being updated. If you maintain any tools there, there are two options for migrating your tools into the new system. There are details, deadlines, and instructions on Wikitech.