Mojang released Minecraft Snapshot 12w07a today adding a new world file format that will implement the increased world height, a new AI system, and some "worse than others" nights in villages.

Last week, lead developer Jens Bergensten first revealed plans for the new increased world height, announcing it would likely be "increased in the future". At the time, he did say that the new world height would update current worlds by adding more air blocks on top, so players would not have to restart a world to take advantage of the new heights.

Staying true to his word, the snapshot will convert the maps you load to a new file format called "Anvil" (256 max height and 4096 block IDs). Jens did say in the patch notes that Minecraft can't use the full range of IDs yet because there are "still some assumptions that IDs above 256 are items."

Below are the patch notes for the development snapshot of week 7, 2012:

•Added new world file format called “Anvil” (256 max height and 4096 block IDs*)
•Multi-player light calculations do no longer cause affected blocks to be transmitted to the clients, instead the clients will recalculate the light on their own
•Villagers will repopulate villages based on how many houses there are available
•Some nights in villages will be worse than others…
•Added a redstone-controlled light source
•Decreased chance for the rare mob drops
•All animals use the new AI system now
After releasing snapshot 12w07a, Jens and the dev team quickly noticed some bugs which they fixed and promptly replaced the update with a newer snapshot. The newer version, technically labeled 'snapshopt 12w07b', fixes the following problems:

•Crash bug corrupting levels when spawning mobs above the 255th block
•Sheep animation is correct in SMP
You can download the Minecraft snapshot 12w07b here:

•Client: http://assets.minecraft.net/12w07b/minecraft.jar
•Server: http://assets.minecraft.net/12w07b/minecraft_server.jar
If you want to revert to the map back to the old format, you need to replace the “level.dat” file with the file called “level.dat_mcr”. The new format will write world regions to files called “*.mca”, so your original regions will remain as “*.mcr”.