This seems as good a thread as any to mention that the gzhttp package in klauspost/compress for Go now supports zstd on both server handlers and client transports. Strangely this was added in a patch version instead of a minor version despite both expanding the API surface and changing default behavior.
About the versioning, glad you spotted it anyway. There isn't as much use of the gzhttp package compared to the other ones, so the bar is a bit higher for that one.
Also making good progress on getting a slimmer version of zstd into the stdlib and improving the stdlib deflate.