Anyone know a decent Windows implementation?

There's a 7zip fork that includes Zstd support, but it can only put Zstd inside a .7z container, which doesn't appear to work with any other tools.

The linked site has windows builds...

True! I suppose what I actually want is a Windows utility that can make a .tar.zst archive, ideally from a GUI.

In the Windows world, archiving and compression are usually in a single file type (.zip, .rar, .7z). Zstd follows the unix style where it can't directly compress folders of files, they need to be in a tar (or other archive format) first. This isn't really an issue on Linux, since Zstd support is built into tar, which ships on pretty much every system.

There haven't yet been any extensions to zip or 7z for zstd support. There is a branch of wimlib that has experimental zstd support, though it's unlikely it will ever be merged into the master branch.

You could make uncompressed zip or 7z files and compress that independently as a zst file, but that's a bit baroque compared to just using tar. :)

7-Zip does often seem bent on supporting everything, I imagine some day in the future it'll support zstd at least as an independent archive, if not extending the Zip and 7z formats as well.

- https://github.com/mcmilk/7-Zip-zstd

The changes to the 7-Zip file format were discussed upstream, and upstream agreed to not tread on the magic values:

- https://sourceforge.net/p/sevenzip/discussion/45797/thread/a...

But ultimately the patches were not upstreamed. It's now onto its second developer:

- https://sourceforge.net/p/sevenzip/discussion/45797/thread/6...