To be fair, both `Analysis` (the type-checker, not necessary at runtime or compile time) and `CodeGen` (the optional JIT engine) have no equivalent in PUC-Rio Lua.

If you look purely at the VM and things necessary to compile bytecode (AST, Compiler and VM) then the difference in code size isn't as stark.

Having worked with both Lua 5.1 and Luau VM code, Luau's codebase is a heck of a lot nicer to work on than the official Lua implementation even if it is more complex in performance-sensitive places. I have mixed feelings on the structural typing implementation, but the VM itself is quite good.