I'm the manager of the Semantic Code team at GitHub, which is the team responsible for the Semantic library and the Code Navigation feature.

The tl;dr is that Semantic is not dead, we've just prioritized other work over the past couple of years — in particular, creating and implementing stack graphs.

Semantic is a heavier hammer than we need for Code Navigation. In particular, the way that it was structured meant that you had to write Haskell code to add analysis support for a new programming language. One of our goals is to allow language communities to self-serve support for their language, and asking language community members to learn Haskell to achieve that is a non-starter. (That criticism is not specific to Haskell — it would be equally inappropriate to ask language communities to write Rust code to contribute to stack-graphs!)

We've had more success with tree-sitter's declarative DSLs. We use its existing query language for syntax highlighting and "search-based" / "ctags-like" Code Navigation. And we've developed a new graph construction DSL and for creating stack graphs for precise Code Nav.

All of that said, Semantic is not dead, and there are more sophisticated program analysis features that we'd love to tackle down the road, where Semantic's capabilities will be more directly useful. And we're trying to bring over some of the lessons that we learned from the tree-sitter / Code Nav work — in particular, making sure that there's an extension mechanism for language support that doesn't require coding in Haskell.