I was very carefully rewatching the video of the reveal and right when Elon starts mentioning safety you can see the schematic of the battery appear behind him. I see 8 battery modules arranged lengthwise as opposed to the 14 on Model S / X. If you look very closely, the actual cells are much larger too. So, their comments at the financial call of Q2 in 2014 where they mention larger cells for Model 3 seems to be true now. Less cells, larger size for more capacity and most likely updated chemistry, made in the US = cost savings they were looking for. Tesla has come through.