MediaWiki 1.21/wmf4

Deployment of MediaWiki 1.21wmf4 to Wikimedia sites
The latest version (labeled "1.21wmf4 ") of MediaWiki, the software that powers Wikipedia and its sister sites, will soon be deployed to all Wikimedia sites in stages.

Deployment will start on Monday, November 12 and continue until Wednesday, November 21 (see the roadmap).

We will continue to deploy the latest software every two weeks. This is intended to minimize disruption and possible issues, and make it easier to identify the cause of problems, since the possibly problematic code will be much more recent.