The Cesium 1.0 release on August 1 will support the latest version of glTF for 3D models. Currently, this is glTF 0.8, which is likely to become the draft glTF 1.0. The online COLLADA-to-glTF converter will also be updated to output glTF 0.8 on August 1.
If you have existing glTF models and upgrade your app to Cesium 1.0, you need to run your original COLLADA models through the converter again to create glTF 0.8 models.
If your app is using a version of Cesium prior to 1.0, it will not be able to load new glTF models generated by the online converter. We, of course, strongly encourage everyone to upgrade to Cesium 1.0.
Also, when it is updated on August 1, the converter will create just a single .gltf file from a COLLADA model. The geometry, textures, shaders, animations, and skins will be embedded in the .gltf file. This is very convenient for deployment.