As Keith put it, "finally got around to some long-needed rebalancing" with this one.
This is a standard update that you can download through the
in-game updater itself, if you already have 4.000 or later. When you
launch the game, you'll see the notice of the update having been found
if you're connected to the Internet at the time. If you don't have 4.000 or later, you can download that here.