It has been almost a month now since we’ve released the STK World Terrain Tileset with water mask support. This left the small terrain supporting a subset of the features available from the World Terrain, and at lower terrain quality. To make the choice terrain produced and maintained by Analytical Graphics, Inc more obvious to the community, we are deprecating the smallterrain tileset effective July, 2015. Cesium will continue to support the heightmap-1.0 spec used by smallterrain.
Since both the heightmap 1.0 and quantized-mesh 1.0 formats are supported by the CesiumTerrainProvider, migrating to the STK World Terrain is as easy as updating the url passed to CesiumTerrainProvider constructor. If you experience any problems migrating to the STK World Terrain tileset, please let us know.