When you visit http://www.opensource.apple.com then you quickly realise that the XNU source code bits for El Capitan are yet to be released, but something tells me that it won’t take long anymore.
Edit: Nope. It took Apple weeks before they released it. Presumably due to code cleanups and possible security related issues, because if you look at the released XNU source code then you’ll see that this is not the code that we are using. Thanks anyway Apple.