"... the model that places the Prius at the top of ASG’s 2019 API, is the Prius Prime. Toyota is bridging the technological gap once again and leading us into the battery electric era with this plug-in hybrid model, featuring 133 MPG-e and a 25-mile all-electric capability. According to ASG, this lithium-ion plug-in hybrid model holds 154 grams of CO2-e emissions per mile driven life-time, a life-cycle carbon footprint that is 48% less than the first generation Prius." 2019 STUDY - Automotive Science Group
I would like to see how much of this improvement is due to having a greener grid as opposed to improvements in the vehicle itself. However, I wasn't able to find a full report that broke down the results in any detail.