Android 4.2.1 started rolling out earlier today to the Nexus 4, 7 and 10. If all you want to do is use your device, that's fine. Those who want to dig deep into the code will be happy to know that now the source code for Android 4.2.1 is available as part of the Android Open Source Project (AOSP).
AOSP's Jean-Baptiste Queru announced the availability of the code for Android 4.2.1 earlier today in the Android Building Google Group. While many users won't initially think there is much benefit to the code being available, anyone who runs custom ROMs should be excited. The AOSP and the source code it provides are very much to thank for the widespread ability of custom firmware.
Queru also stated that Android 4.2.1 factory images will be available in coming days, which may be of more use to those of use who aren't coders. There aren't many updates in 4.2.1, as it's mainly a bugfix release, but having the most up to date release is useful for both ROM creators and app developers.
If you want to take a look at the code for yourself, head to the Android Building group in the source links below.
Are you planning to download the code?