MediaWiki 1.27.0-wmf.1 (note the version format change) was deployed to WMF wikis last week. I was supposed to send an email about that last week, but I didn't. My apologies for the late announcement.

The highlights for Echo and Flow are:

Various fixes for the new notification badges, most notably:

Middle-clicking and Ctrl+clicking on the badge now always works.
The "talk" link no longer disappears when the orange "You have new messages" bar is dismissed.
The alerts badge no longer briefly flashes red before becoming grey.

Editing topic summaries in Flow now uses the new editor system.
Links added to the history of a Flow topic when it is resolved no longer go to error pages.
"Null" edits (edits without changes) are no longer saved by Flow. (Although this doesn't seem to quite work just yet.)
Names of authors are now bidi-isolated in Flow.

wmf.1 was deployed according to the normal deployment schedule:

Tuesday 18:00-20:00 UTC: test wikis (mediawiki.org, testwiki, test2wiki and testwikidata)
Wednesday 18:00-20:00 UTC: non-Wikipedia wikis
Thursday 18:00-20:00 UTC: Wikipedias