Comment by wahern

gzip/deflate also supports dictionaries[1], and in a roughly similar manner--you feed the encoder/decoder the dictionary data purely for the side-effect of updating internal state, without generating any output. But just as zstd supports much larger windows, it also supports much larger dictionaries.

[1] There just aren't any good open source tools for creating that dictionary (but see https://blog.cloudflare.com/improving-compression-with-prese...), few examples of how to use the low-level library APIs to manage dictionaries (see, e.g., deflateSetDictionary at https://www.zlib.net/manual.html#Advanced), and common utilities don't expose this functionality, either.