Android build numbers generally start with the same letter as the name of the current version of Android. For example, the latest build of KitKat is KOT49H (technically KVT49L for only the Nexus 7 LTE). However a couple of builds are appearing that start with the letter “A” as in ACU50C and ACU56E. This information comes from the idea133-weekly-release, which is for developers.
At this point, you would expect the next version of Android to start with the letter “L” since they have been going in order since Cupcake. Is Google planning something different? We’re not really sure, but here is how the build numbers break out.