With the merge of Gerrit change 216048,[1] the 'generatexml' parameter to action=parse, action=query&prop=revisions, and action=query&prop=deletedrevisions is deprecated in favor of a new 'parsetree' prop.
This should be deployed to WMF wikis with 1.26wmf13, see https://www.mediawiki.org/wiki/MediaWiki_1.26/Roadmap for the schedule.