The various major incarnations of Inform are by established convention usually referred to as Inform 1, Inform 2…Inform 6, Inform 7 (no ‘version’ in the name).
Of course, Inform 7 is entirely unlike all the others.
On top of that, Inform 7 in particular has a long line of versions as the language has developed and releases have been made. These were historically labelled with an alphanumeric build code, such as 5U92 or 6M62.
With the release of open-source Inform 7, build codes were retired to a back seat with semantic version numbers being introduced and retrospectively fitted to all past releases. So, the first public release of Inform 7 (build 3K27) became version 1.1 of Inform 7 and the first open-source release was version 10.1.0 of Inform 7.
Graham Nelson has suggested that the ‘7’ be perhaps dropped as redundant, leaving just plain ‘Inform version 10.1.2’ but most prefer to keep it to make it plain that one is not talking about a version of Inform 6.