In change I7a3d7b6e[1] which was recently merged, the ApiPageSet module received a major overhaul. In particular, the parameters to the constructor have changed, and it now extends ApiBase rather than ApiQueryBase. These changes will not affect API clients, but any third-party API modules that use ApiPageSet will need to be updated.
Also as part of this change, ApiQuery is losing its newGenerator() and executeGeneratorModule() methods, and ApiQueryGeneratorBase's setGeneratorMode() is gaining a required parameter. These methods are unlikely to have been used in non-core code.
This brings with it enhanced functionality: non-query actions using ApiPageSet may now use generators. The core action=purge and action=setnotificationtimestamp modules have already been enhanced in this way.
This change should go live on WMF wikis with 1.21wmf10; see the roadmap for details.[2]
[1]: https://gerrit.wikimedia.org/r/#/c/44087/ [2]: https://www.mediawiki.org/wiki/MediaWiki_1.21/Roadmap