AFAIK it is a common experience that both C and C++ code tend to become fewer LOC in a move to Rust, a lot of it due to stuff like serde that greatly reduces boilerplate. It probably depends on your application and program size, though. I'm sure that if you're doing a lot of pointer wrangling or something it won't be smaller in Rust, while if your C program was just a bunch of SIMD intrinsics anyway like a lot of high performance code is now it'll probably be basically the same length.