Regarding semantic versioning: what would constitute a breaking change?

I think it makes sense to increase the major / minor numbers based on the importance of the release, but this is not semver.

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.

Or drop the pretext of version numbers entirely since they're meaningless here and go back to classics like Gemini Experience, Gemini: Millennium Edition or Gemini New Technology

Would be confusing for non-tech people once you did x.9 -> x.10

What would a major version bump look like for an llm?

Going from English to Chinese, I guess? Because that would not be a compatible version for most previous users.