Pageview information about Wikimedia sites, which has been available for a while through the standalone Pageviews REST API [1], is now available in the action API as well, through the prop=pageviews [2], list=mostviewed [3] and meta=siteviews [4] API modules. An example:

The new API modules basically act as a proxy to the REST API, and are meant as a less flexible but more convenient alternative for people who already use the action API.