Maya 2023.2 includes MtoA 5.2.0 for Arnold 7.1.3 which provides improved volume rendering, improvements to the USD procedural and the Hydra Render Delegate, as well as an improved viewport experience.
Improved Volume Rendering: New dual lobe phase function parameters in the volume shader make it easier to render realistic clouds, and new modes for controlling the scaling of the emission can improve the look of emissive volumes.
USD Improvements: The Render Delegate now supports Cryptomatte, mesh lights, color management, light filters, light shaders, and nested instances as well as pinned curves and overscan. Velocity motion blur, NURBS curves, and UsdPreviewSurface displacement are now supported in both the Render Delegate and the procedural. In addition, you can now export Arnold shaders directly through Maya USD.
Improved Arnold Viewport experience: A new toolbar added to all model view panels makes it easier to run and control the Arnold Viewport Renderer, the Maya Render view has been replaced with Arnold Render view for Arnold Renders and IPR, (except for Render Sequence), and 5.2.0 also adds support for the native Emit Specular and Emit diffuse options on Maya lights.
See the Arnold for Maya release notes for the full list of recently added features and bug fixes for versions 5.2.0 and earlier.