What's new in ArcGIS Spatial Analyst 10.1
For the ArcGIS 10.1 Spatial Analyst extension, the scope of functionality is generally similar to what was available in ArcGIS 10.0. However, there have been general improvements in stability and performance.
The interactive tools from the Spatial Analyst toolbar have been updated to operate on the data within the extent of your ArcMap window and at the screen resolution. This provides the benefit of being able to respond quickly even on very large input raster datasets.
Spatial Analyst tools can now read and write rasters to an in-memory workspace.
The version of ANUDEM used in the Topo to Raster and Topo to Raster by File tools has been updated to version 5.3. For more information, see What's new in the Spatial Analyst toolbox.