Arnold for Katana (or KtoA) provides a bridge to the Arnold renderer from within the standard Katana interface.
Natural integration with Katana nodes, scenegraph, and scripting.
Multi-threaded scene translation, made possible by Geolib3 in Katana 2.
Bundled Arnold, shaders, and plugins for a smooth out-of-the-box experience.
Support for the latest Arnold 4.2.x series.
Improved interactivity for live rendering (IPR) allows look changes to be rapidly previewed.
Ultra-fast OpenVDB volume rendering.
Works with third-party shaders and renderer procedurals (for hair, etc).
Render outputs and AOVs, including Deep EXR.
Supports the curves location type in Katana for hair rendering.
Many light types and light filters supported, as well as interactive modification of lights.
Object parameters and global options better match what is available in Arnold.
Improved documentation within Katana (args files).