Two differences:

(1) This feature only requires regex-guided generation. We have a PR for BNF sampling that is about to be merged. (2) ggml loops over the entire vocabulary (~50k tokens) at each step, which introduces a noticeable overhead, and makes it unusable for complex grammars. Our method works by building an index at initialization, and build the masks at each step with a dictionary lookup. Once the index is built, generation is just as fast as standard generation. Doesn't depend on the complexity of the grammar, the size of the LLM or its vocabulary size.