Sorry to all people testing this feature, starting from the next nightly your current cash will be divided by 65536 due to a bug in the savegame loading code. Games saved before the 64bit cash feature would have their last 16 bits cut off from the cash amount, so I had to move the variable over a bit, which will unfortunately also divide the amount.
Actually I just realized that you can probably keep most of it. It should work to load the pre-r463 save in beta 5 (or any non-64bit-cash nightly), then save it there, and when you reload it in the latest nightly you should have 2bn again.