Google has released the source code of all the versions of the Android operating system, until Gingerbread (Android 2.3). However, they did not release the source code of Honeycomb (Android 3). Google had said that Honeycomb is the exception and that the versions of Android released after that will be open source again.
After the release of the latest version of Android yesterday - Android 4.0 Ice Cream Sandwich, rumors started floating around that Google might go back on their words and not release the source code of ICS (Ice Cream Sandwich) afterall. This was based on the fact that even though the ICS SDK has already been made available, the source code is nowhere to be found.
Jean-Baptiste Queru of Google has confirmed today on Google+ that the rumors of ICS being closed source is untrue. He said that Google is releasing the source code of ICS as originally intended.
This is what's been consuming my entire life for the last 6 weeks. The Android Open-Source Project is distributing source code again.
Get also a glimpse about the future (yes, that means ICS will be coming to AOSP).
Google has not announced the release date for the source code of ICS, but if the past releases are any indication, they generally release it just after the Nexus device has actually been released. The Samsung Galaxy Nexus - the first phone to run ICS - will be available next month. So, we can safely assume that we will see the ICS source code in about a month.