I just added zstd to gentoo-sources which will apply to gentoo-sources kernels >=5.6.4 when the ‘experimental’ use flag is enabled.
zstd is described here as “…a fast lossless compression algorithm, targeting real-time compression scenarios at zlib-level and better compression ratios. It’s backed by a very fast entropy stage, provided by Huff0 and FSE library.”
You can read more about it here.
Thanks to Klemen Mihevc for the request