Generation Amiga has reported today a tweet from Hacker Fantastic saying that the Amiga OS source has been leaked, including both Kickstart and Workbench. Looking at the @hackerfantastic's tweet, there is another user with the handle @TheWack0lian that offers a link to download the OS in a 130MB tar file which expands to 540MB of source code.
Apparently the source code is really related to Amiga OS. The tar file name refers to OS 3.1 but folders from the source code refers to version 4, which could mean the source code is pretty much up to date.
From what I can gather, it's not fully 100% complete, but it's still a pretty significant leak. With the number of times this software has changed hands, it's remarkable it's taken this long.