As I see it, if it uses a similar training approach and is expected to be better in every regard, then it's a minor release. Whereas when they have a new approach and where there might be some tradeoffs (e.g. longer runtime), it should be a major change. Or if it is very significantly different, then it should be considered an entirely differently named model.
I think it makes sense to increase the major / minor numbers based on the importance of the release, but this is not semver.