The .ass extension stands for Arnold Scene Source.
There are three ways to export assets to .ass files:
You can export single objects as well as a whole hierarchy made out of multiple objects.
Important note: During export, Arnold will honor its current render settings, for example, whether motion blur is enabled. You should think about whether you will want to use motion blur (and so enable it or not) before you export objects to be used as stand-ins later on.
2. From the script editor, with the command
SITOA_ExportScene(frameStart, frameEnd, frameStep, createStandIn, selectionOnly, filename)
Filename supports tokens. When exporting a sequence, you can use the [Frame] token in the filename, to have it resolved correctly at each frame.
SITOA_ExportScene(1, 10, 1, false, false, "/usr/tmp/Test.[Frame #4].ass);
Exports 10 .ass files, named /usr/tmp/Test.0001.ass, /usr/tmp/Test.0002.ass, etc.
3. From the rendering options, using the Export Frame or Export Animation buttons in the ASS Archives tab.