The git repo is here: https://github.com/scip-code/scip

Looks like it's defined using protocol buffers, with "rich Go and Rust bindings" and links to implementations for many other languages.

I can’t speak for the Go bindings, but using the Rust crate has been pretty clean. Haven’t really felt the need to dip into deserializing raw .scip file in the time that I’ve been working with SCIP.