Microsoft reached the milestone in August, as promised most recently. With release still slated for spring 2016, this provides a longer-than-normal feedback period for customers to evaluate and validate the release.
The IT Preview allows organizations to focus on investments in infrastructure and deployment features, and Microsoft is asking customers to install the preview in a test environment and perform test migrations. The preview is not meant for production environments, and will not be upgradeable to the final release of SharePoint 2016.
While the IT Preview sports some new user-facing functionality, including an App Launcher and improved mobile experiences, Microsoft emphasizes that this released does not reflect the featureset that will be included in SharePoint 2016 when it is released. There will likely be additional preview releases that will incorporate "business value" features and capabilities between now and the final release.
The release is detailed in a blog post on Office blogs by Bill Baer, Senior Technical Product Manager.
You can download the preview from Microsoft's Download Center.
Join Bill for a live look at the preview on a special episode of Tech Talk with Bill Baer on Monday at 12:00pm Pacific, 3:00pm Eastern.