"But what we found with these neural networks is, if you use 32 bits, they're just fine. And then you use 16 bits, and they're just fine. And then with eight bits, you need to use a couple of tricks and then it's just fine.

And now we find if you can go to four bits, and for some networks, that's much easier. For some networks, it's much more difficult, but then you need a couple more tricks. And so it seems they're much more robust."

That will be really interesting for FPGAs, because the current ones are basically oceans of 4-bit computers.

Yes, you can gang together a pair of 4LUTs to make a 5LUT, and a pair of 5LUTs to make a 6LUT, but you halve your parallelism each time you do that. OTOH you can't turn a 4LUT into a pair of 3LUTs on any currently-manufactured FPGA. It's simply the "quantum unit" of currently-available hardware -- and it's been that way for at least 15 years (Altera had 3LUTs back in the 2000s). There's no fundamental reason for the number 4 -- but it is a very, very deep local minimum for the current (non-AI) customers of FPGA vendors.