I use Emacs with lsp-mode (Language Server Protocol) a lot (for haskell, rust, elm and even java) and there was a dramatic speedup from Emacs 27 onwards when it

I use Emacs with lsp-mode (Language Server Protocol) a lot (for haskell, rust, elm and even java) and there was a dramatic speedup from Emacs 27 onwards when it started using jansson JSON parsing. I don't think it's the bottleneck at the moment, but it's good to know there are faster parsers out there. Had a small search but couldn't find any plans to incorporate simdjson, besides a thread from last year on Emacs China forums.