How much Opensource is Cesium JS

I am a big fan of the features provided by Cesium Ion platform.

We are presently working on integrating the cesium js library into a different web application for a commercial application and we intend to use only open source libraries.
The documentation on which features are open-source and which are under the cesium ion platform was a little confusing.

We would request support on listing which features are open-source commercial or if a list already exists.
For example:

  1. Is the Cesium 3D viewer open source with Cesium JS?
  2. Is the default globe used open-source or do we have to integrate different open source globes? (e.g. QGIS or Openstreet map )

The Cesium platform follows an open-core business model with open source runtime engines such as CesiumJS and optional commercial subscription to Cesium ion.

CesiumJS can stream 3D content such as terrain, imagery, and 3D Tiles from the commercial Cesium ion platform alongside open standards from other offline or online services. We provide Cesium ion as the quickest option for all users to get up and running, but you are free to use any combination of content sources with CesiumJS that you please.

The Offline Guide gives a few pointers on how to use CesiumJS with offline sources, but that can be extended to other online services as well. Let us know if you’re looking for pointers on any data type or file format in particular.