“Can copyrighted source code be laundered through an LLM and come out the other end as a fresh work of authorship, eligible for a new copyright, copyright holder, and license terms?”
To make things even worse, I created a chardet-rust port using Kimi K2.5 model based on the chardet 7.0 (the new AI implementation) which is a dozen of times faster...which license can I use for my version? 
US courts have already ruled that works created by a program (or a chimpanzee) cannot be copyrighted. So, regardless of the question of whether the new work can even be created from an existing copyrighted source, they can’t claim ownership or license it. If it was anybody but the chardet maintainers, this surely does not meet the “fair use” claim that the LLM creators have used for stealing millions of books (apparently on the “If You Steal From One Author, It’s Plagiarism; If You Steal From Many, It’s Research” principle). Since they used their own code, I guess they avoid the copyright violation, but even so their use is not consistent with the GPL.