Silicone anode is supposed to increase capacity by 30% when fully utilized.
Tick to 90kWh used a tiny bit of silicone (5%) in anode, just to feel the waters and see how it behaves in reality.
Now they are getting more data, they feel confident to use a bit more.
If they jumped right into it, you would get 110kWh capacity overnight from same 7104 cells and 85kWh from 5600 cells.
Silicone comes with its own can of worms though, cycling degradation being one of the nastiest.
So: S85 is ~80,701Wh. If we assume a 100D battery is 100,000Wh, then: 100,000Wh/80,701Wh=1.239. That's an increase of 24%. You said the max is around 30%.
Now, let's look at the ratio of the S90D to the S85D battery: 288 EPA rated miles / 270 EPA rated miles = 1.067. That's an increase of 7%, which is what they did in the 90, possibly, anyway.
So, if Tesla has been doing studies on using Silicone anode, perhaps they're ready to increase the anode effectiveness to about 3.6x of what they already have.
There are a few other things I could wildly connect with no real foundation on why they have to be connected:
1. They have done some careful charger programming in the latest firmware update, that is much more careful about ramping up. Perhaps they have better profiles about how to charge their Silicone anode batteries without as much degradation. Similarly, they have been adjusting the temperatures and aggressiveness that the batteries can take regeneration from slowing down.
2. Super wild crazy ass speculation that is most likely untrue: What if all the new 90D's coming off the line in the last couple of weeks are actually 100D's with the more delicate battery chemistry, and Tesla is in a BIG hurry to send updates to those cars to not over-tax the new delicate chemistry?
I've had a boring life, so I need the fun speculation. Please don't blame me for being excessively creative.