Indeed a developer owns copyright over the source code and on the compiled binaries, because there is no expansion happening here but just a translation from one format into another, the kind of thing that has been ruled copyrightable since copyright exists. The same goes for translations from one human language into another, and anybody with knowledge of more than one language will be happy to acknowledge that translating is hard work. Even so, the translator does not hold copyright on the result, at best they can say they have created a derived work and it is the original author that continues to hold copyright.

Compilation and translation happen in a generic manner and does not rely on a mountain of other IP, it is really just a transformative tool that happens to do something useful, someone constructed it to be a very precise translation to the point that any mistakes in it are called bugs and we fix them to ensure the process stays deterministic. Translators try hard to 'get it right' too: to affect the intentions of the original author as little as possible.

When you use a model loaded up with noise or that you have trained exclusively on code that you actually wrote I think a strong case could be made that you own the copyright on that work product. But when you train that model on other people's work, especially without their consent or use a model that has been trained in that way you lose your right to call the output of that model yours.

You did not write it, and the transformative process requires terabytes of other people's IP and only a little bit by you.

As soon as you can prove that your contribution substantially outweighs the amount of IP contributed in total you would have a much stronger case.

> If that were true, a developer may own copyright over the source code, but nothing on the compiled binaries, and I could download practically all software available as compiled binaries and use for free.

If the compiled binaries (output) were produced by running the input (source code) over every program written, then sure.

But that's not what's happening with compilers, is it? The output of a prompt is dependent on copyrighted work of others every single time it is run.

The output of a compiler is not dependent on the copyright output of every other program.