According to the Fiddler Wiki:
SAZ files are simply specially formatted .ZIP files. If you rename a
.SAZ file to .ZIP, you can open it for viewing using standard ZIP
Inside a SAZ file, you will find:
_index.htm - an optional file containing a human readable version of the Session List. This file is not processed when loading a .SAZ file
and exists solely for manual examination. [Content_Types.xml] — (Added
in v126.96.36.199) A metadata file which specifies a few MIME types so the
archive can be read by System.IO.Packaging or other clients that
support the Open Packaging Conventions. a raw folder - containing
files representing each web session. Inside the Raw folder, there will
be three files for each web session.
sessid#_c.txt - contains the raw client request. sessid#_s.txt -
contains the raw server request. sessid#_m.xml - contains metadata
including session flags, socket reuse information, etc. The SAZ/ZIP
file's comment field contains information about the version of Fiddler
that generated the archive.
SAZ files should always be forward/backward compatible, although some
features may be missing (e.g. socket reuse information) when loading
older files into the newest versions of Fiddler.
SAZ Files MIME types are: application/x-fiddler-session-archive