From MSDN: DeflateStream Class
DeflateStream cannot be used to compress files larger than 4 GB.
Are there any other implementations for .NET without the 4 GB limit?
NOTE: I really need to decompress a file in GZ format with content larger than 4 GB. Can any code do that?
There is sample code at CodeProject using the 7-Zip library.
The license is open, so you should be able to use this in your project.
7-Zip also supports GZ files.