from https://www.lua.org/versions.html:

The releases of Lua are numbered x.y.z, where x is the series, x.y is the version, and z is the release.
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Different releases of the same version correspond to bug fixes. Different releases of the same version have the same reference manual, the same virtual machine, and are binary compatible (ABI compatible).
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Different versions are really different. The API is likely to be a little different (but with compatibility switches), and there is no ABI compatibility: applications that embed Lua and C libraries for Lua must be recompiled. The virtual machine is also very likely to be different in a new version: Lua programs that have been precompiled for one version will not load in a different version.