On the Bitmain Website they now list the Antminer S9i how is this different than the S9?
The main hardware difference is, the hash board heat sinks are different heights! You cannot use all 3 S9i hash boards in a regular S9. The S9i heat sinks are 3mm smaller on the bigger heat sink side(silver) and the smaller brown heat sinks on the other side are 3mm taller. You can only fit 2 S9i hash boards in a S9 housing.
S9i is an upgraded version of s9, shares almost the same hashrate 13TH/s+-10% and power consumption at 1300w+-10%, S9i is cheaper than S9.
Same difference minus the 20 Watts of savings as mentioned above. It also seems they are dropping the price and moving bountiful amounts compared to before. Sites like Blokforge https://blokforge.com/product/bitmain-antminer-s9i-14-th-s/ are carrying hundreds of these units unlike any time in the past where units were limited to 1 or 2 per person.
Only difference is price -- It is exact the same machine! They have changed software a drop to save about 20 watts per unit that means about $1 per month savings just about no difference.
Just a marketing game they will be releasing the newest hardware soon, JUNE I imagine .. for September shipping!