A file with the CPGZ file extension is a UNIX CPIO Compressed Archive File. It is the result of a GZIP-compressed CPIO (Copy In, Copy Out) file.

A CPIO archive is uncompressed, so GZIP is applied to the file so that it can be compressed to save disk space. These archives can contain software programs, documents, movies, and other types of files.

TGZ is a similar format that compresses a TAR file (which is also an uncompressed file container) using GZIP compression.

CPGZ files are commonly seen on macOS and Linux operating systems. The ​ditto command-line tool is one way to open one on those systems.