TWSBI is changing the nibs in their Vac-700 from Bock to Jowo, and in the interim there will be one of each shipped with the pen. If you want to swap the Bock (on the pen) with the Jowo (which comes in a separate nib unit), then you'll want to see this video. It's a little different than when you purchase a TWSBI nib unit by itself (not yet available for the Vac-700), which comes with the grip section of the pen. This nib unit only comes with the nib, feed, and housing, and you'll need to pull the nib out of the housing in order to swap it. It's not hard to do, but there are a couple of little things I needed to point out.
All TWSBI Vac-700's should be coming with the additional Jowo nib now, but you'll want to check with your retailer of choice to make sure they have the Jowo nibs if you're buying a smoke, amber, or blue one. Clear pens already come with the Jowo nib on it, so you will not need to do this swap if you're buying a Clear Vac-700. If you have already purchased a Vac-700 and are having trouble with your nib, send an email to TWSBI at email@example.com and they will help you out with that and get you a new Jowo nib unit if needed.