It's from the same team (which I am the manager of), but it's not using that same codebase. In Semantic, you would have to write Haskell code to add support for a new language, and we've found that the declarative DSLs that tree-sitter provides are a lower barrier to entry. (Semantic also uses tree-sitter for the parsing step, btw.) We do still have plans for Semantic, but our stack graph code does not live there.
[Edit] Also, the stack graph implementation is also open-source, just like Semantic, and we do our development on the core algorithms directly there. The Python extraction rules have not yet been moved over to the public tree-sitter-python language repo, but that's on the docket. Future language support would happen directly in each language's public open-source tree-sitter repo.
Are the extraction rules in the stack-graphs repository or other public repository, or in a private repository? It would aid understanding to have a fuller working example.
They're currently in a private repo, only because they use an old crusty implementation of the graph DSL. We're porting them over to the open-source graph DSL (tree-sitter/tree-sitter-graph), and we'll add them to the tree-sitter-python repo as part of that effort. As mentioned above, future language development will happen directly in the per-language tree-sitter repos using the open-source graph DSL implementation.
[Edit] Also, the stack graph implementation is also open-source, just like Semantic, and we do our development on the core algorithms directly there. The Python extraction rules have not yet been moved over to the public tree-sitter-python language repo, but that's on the docket. Future language support would happen directly in each language's public open-source tree-sitter repo.
https://github.com/github/stack-graphs/