Not really pytroch related it seems ?
Are you referring to this ? https://fileinfo.com/extension/ark 2
If so… it’s a pretty arcane format, I’m pretty sure people switched to .zip and .gzip a few decade ago, if you need it for some reason you can use arc (https://sourceforge.net/projects/arc/ 1), at least on linux (but should work on OSX and windows as well I’d assume)
Just output whatever you have to a text file and then use the arc tool to compress it. There’s also a python library for it seemingly: https://pypi.org/project/arc/ 2, but I’m not sure if it actually works.