Changes later this week

Recurrent item The new version of MediaWiki will be on test wikis and MediaWiki.org from 20 October. It will be on non-Wikipedia wikis and some Wikipedias from 21 October. It will be on all wikis from 22 October (calendar).
Future changes

1. You will be able to read but not to edit the wikis for up to an hour on 27 October around 14:00 (UTC). It will probably be shorter than an hour. 
2. Advanced item In the AbuseFilter extension, the rmspecials() function will be updated soon so that it does not remove the "space" character. Wikis are advised to wrap all the uses of rmspecials() with rmwhitespace() wherever necessary to keep filters' behavior unchanged. You can use the search function on Special:AbuseFilter to locate its usage. 
3. Some gadgets and user-scripts use the HTML div with the ID #jump-to-nav. This div will be removed soon. Maintainers should replace these uses with either #siteSub or #mw-content-text. A list of affected scripts is at the top of phab:T265373.