The new version of MediaWiki will be on test wikis and MediaWiki.org from 14 June. It will be on non-Wikipedia wikis and some Wikipedias from 15 June. It will be on all wikis from 16 June (calendar).
Some wikis will be in read-only for a few minutes because of a switch of their main database. It will be performed on 14 June at 06:00 UTC (targeted wikis). 
Starting on Wednesday, a new set of Wikipedias will get "Add a link" (Abkhazian Wikipedia, Achinese Wikipedia, Adyghe Wikipedia, Afrikaans Wikipedia, Akan Wikipedia, Alemannisch Wikipedia, Amharic Wikipedia, Aragonese Wikipedia, Old English Wikipedia, Aramaic Wikipedia, Egyptian Arabic Wikipedia, Asturian Wikipedia, Atikamekw Wikipedia, Avaric Wikipedia, Aymara Wikipedia, Azerbaijani Wikipedia, South Azerbaijani Wikipedia). This is part of the progressive deployment of this tool to more Wikipedias. The communities can configure how this feature works locally. 
The New Topic Tool will be deployed for all editors at Commons, Wikidata, and some other wikis soon. You will be able to opt out from within the tool and in Preferences. 
The next open meeting with the Web team about Vector (2022) will take place today (13 June). The following meetings will take place on: 28 June, 12 July, 26 July.
By the end of July, the Vector 2022 skin should be ready to become the default across all wikis. Discussions on how to adjust it to the communities' needs will begin in the next weeks. It will always be possible to revert to the previous version on an individual basis. Learn more.
Some recent database changes may affect queries using the Quarry tool. Queries for site_stats at English Wikipedia, Commons, and Wikidata will need to be updated. Read more.
A new user_global_editcount variable can be used in abuse filters to avoid affecting globally active users. 
Changes later this week
The new version of MediaWiki will be on test wikis and MediaWiki.org from 21 June. It will be on non-Wikipedia wikis and some Wikipedias from 22 June. It will be on all wikis from 23 June (calendar).
Users of non-responsive skins (e.g. MonoBook or Vector) on mobile devices may notice a slight change in the default zoom level. This is intended to optimize zooming and ensure all interface elements are present on the page (for example the table of contents on Vector 2022). In the unlikely event this causes any problems with how you use the site, we'd love to understand better, please ping Jon (WMF) to any on-wiki conversations. 
Parsoid's HTML output will soon stop annotating file links with different typeof attribute values, and instead use mw:File for all types. Tool authors should adjust any code that expects: mw:Image, mw:Audio, or mw:Video.