But I cajoled the dealer into giving me the fast charging update.
I stopped up at the EA DCFC 350 KW fast charger up in Mojave and it was the same 50-53 KW charging when I had about 80 miles left at the start of charging. Same as before.
Of course it was not "cold weather" up their either!
There may be another difference (the behavior is this way on the 2020 Bolt) : change of the charging profile. Before the 2020 model, DCFC would "step down" the charging rate when certain points were hit. IIRC, at around 50-55 % SoC, the charge steps down very quickly from 150A (~55 kW) right down to around 105A (~38 kW). At around ?75? % SoC, the charge steps down very quickly from 105 (~38 kW) right down to around 65A (~24kW). Those numbers are from memory, so they aren't exact, but they are close. The 2020 charge profile is more of a curve. It still starts downward around 50%, but it *slowly* lowers the amps in a curve, so the kW rate slowly declines, meaning an overall faster charge. The *rate* of charge didn't increase, but the charge rate "curve" over "step" drops will not to a faster charge.
I don't know if you have an OBD reader and app for the Bolt, but you could check this out if you have one the next time you fast charge.
Now the difference is negligible if you are charging on a 100A charger, but if you use one of the newer ChargePoint 250 units, or the Electrify America 150 kW chargers, you will have full speed charging up to about 50% and can watch to see if the amps drop to 105 in a handfull of seconds or if the amp rate slowly decreases over a few minutes. One could also watch the DCFC displays with amps and/or kW and % of battery and watch the rate drop to figure out if that 2020 functionality was included in the update.