> So, when this gets to a court (which it will, it's not a question of "if"), the court will consider how necessary the source work was to what you did. If you used it for a direct translation (eg from C++ to Go) then you're going to lose. My prediction is that even using it in training data will be cause for a copyright claim.

This has a lot of similarity to when colorization of film started popping up. Did colorizing black and white movies suddenly change the copyright of the film? At this point is seems mostly the courts say no. But you may find sometimes people rule the other way and say yes. But it takes time and a lot of effort to get what in general people want.

But basically if you start with a 'spec' then make something you probably can get a wholly owned new thing. But if you start with the old thing and just transform it in some way. You can do that. But the original copyright holders still have rights too to the thing you mangled too.

If I remember right they called it 'color of copyright' or something like that.

The LLM bits you are probably right. But that has not been worked out by the law or the courts yet. So the courts may make up new case law around it. Or the lawmakers might get ahead of it and say something (unlikely).

A work could even have two copyrights! Copying a colorized film could require the permission of both the studio that made the film, and the studio that colorized it.