Their GitHub readme has a section answering this. https://github.com/antlr-ng/antlr-ng#future https://github.com/antlr-ng/antlr-ng#future Basically they feel

Their GitHub readme has a section answering this. https://github.com/antlr-ng/antlr-ng#future https://github.com/antlr-ng/antlr-ng#future Basically they feel the main problem with the original antlr is it’s being stifled by its batteries included nature. They’re hoping that splitting it will make each of the runtimes more agile. They don’t mention why the core was rewritten rather than just forking the original.