The second beta of the next generation ArcGIS API for JavaScript is now available.
Version 4.0 beta 2 of the ArcGIS API for JavaScript has been released. Read about it in the blog at http://blogs.esri.com/esri/arcgis/2015/11/19/arcgis-api-for-javascript-4-0-beta-2-released/ or check out the details in the Whats New.
This includes support for vector tiles, a new popup design, support for local scenes, reading of web scenes and more.