I have asked Soybeen about it, and he hasn't answered yet. I have a guess that it holds infinite items, but that's just an assumption. All I know is, nobody yet has even reached level 1000, so we don't know what kind of "Godliness" this bag is really.
I have the bag and it hold 3,000 storage. Because of the bag I hold about 3,000 emeralds and mag and practically a lot of stuff. The bag is so OP. I got it off the market in booga for 4,000 coins then Soybeen took it away, but I got another one.