Does GitHub currently use tree-sitter for syntax highlighting? If yes, are the libraries open-source? Thanks :)

For some languages, yes. https://news.ycombinator.com/item?id=26227214

> If yes, are the libraries open-source?

They are! tree-sitter itself is open-source [1], as are all of the language parsers we've listed on the homepage [2]. The syntax highlighting support is documented here [3].

[1] https://github.com/tree-sitter/tree-sitter

[2] https://tree-sitter.github.io/tree-sitter/#available-parsers

[3] https://tree-sitter.github.io/tree-sitter/syntax-highlightin...