Earlier this week, Apple published new documentation regarding the Apple News Format (via Benedict Evans), which will allow all publishers to deliver native articles with richer experiences to their Apple News channels. Currently, only selected publishers have access to the Apple News Format.
In addition, Apple has detailed an API for publishers on Apple News, which can be used to publish Apple News Format articles as well as "retrieve, update, and delete articles you’ve already published, and get basic information about your channel and sections". An API reference is available here, and Apple has included links to CMS plugins for WordPress and Drupal.
Last, Apple has also released a News Preview tool for OS X to preview Apple News Format documents in the Xcode simulator. It's available as a beta download here.
You can read our review of Apple News for iOS 9 here.