LuaJIT is an entirely different VM. It is binary compatible with Lua 5.1.x modules (shared libraries) and can run most Lua 5.1 and 5.2 code. A good amount of

LuaJIT is an entirely different VM. It is binary compatible with Lua 5.1.x modules (shared libraries) and can run most Lua 5.1 and 5.2 code. A good amount of the 5.2 changes, specifically those which do not break 5.1 code, have been added to the VM.