The Windows XP source code was allegedly leaked online

[nulli]

The Windows XP/2003 source is a nice addition to the collection. But these days its really not a big whoop if you have the Windows 2000+WRK sources. You can use the XP source to get some more hints about how something used to work. Which can help a bit. But there is a lot of internals that have changed in Windows 10 especially.

And with the powerful decompilers we have today combined with debug symbols it's not that hard to figure out what a Windows function does. I have recreated (yes, as in made fully working C/C++ code based on disassembly of Windows 7-10) more than 300 Windows API functions this way.

Worth getting your hands on? Sure! the source is of course interesting if you develop for the Windows platform and like to get down and dirty.