Gzip just isn't specified well enough to be fully reproduceable. Gzip is technically only a file format specification, with multiple compression algorithms all

Gzip just isn't specified well enough to be fully reproduceable. Gzip is technically only a file format specification, with multiple compression algorithms allowed. Also Gzip includes metadata about the compression like a timestamp for when the file was compressed, and bits for which OS was in use when the file was compressed, etc. so the out put is never 100% the same, though it ought to be easy to work around that part.