The Lua API version currently used in darktable 3.4 is 6.1.0.
The Lua API is currently at version 6.2.0 in the development branch of darktable (currently 3.5). All changes for version 6.2.0 will be identified as such until version 6.2.0 is included in a darktable release.
+The Lua API is currently at version 6.2.1 in the development branch of darktable (currently 3.5). All changes for version 6.2.+ will be identified as such until version 6.2.+ is included in a darktable release.