Here's what Curbed had to say about Lumina today:
http://sf.curbed.com/archives/2013/1..._more.php#more
Currently: Excavation of the massive site covering over half a SoMa block is moving along. Support walls along the perimeter are up, clearing the way to excavate the remainder of the site and begin prep for foundation pouring, which will still be a while off. Don't expect to see this one rise above the ground until early-to-mid 2014, while the sales office will open in summer 2014.
Interesting photos at link. From my perch, it appears they are nearly 3 floors deep and mostly dug out at that point. With a matte pour, then they are really only ~2 floors deep, but I would think for garage purposes they will want to dig out one more floor so that they really end up with 3 subterranean parking levels. This would also explain the 43 and 38 story figures, as the math on heights doesn't add up that these towers are 43 and 38 stories above ground. More like 40 and 35 with 3 below-ground parking levels. I suspect cranes will be up by year end.