Apple’s first Mac with its own ARM processor will be the 13.3-inch MacBook Pro, according to analyst Ming-Chi Kuo (via iMore). He believes that production of that model will start in Q4 of 2020, with an A-series powered MacBook Air arriving shortly afterwards either in Q4 2020 or early 2021. Apple will also release 14- and 16-inch versions of the MacBook Pro with its own silicon that will enter production in Q2 or Q3 of 2021.
Apple already said that it would ship its first ARM-powered Macs by the end of 2020, but the big mystery was which model would arrive first. It was logical to expect a more lightly powered, lower-stakes productivity PC like a 12-inch MacBook or MacBook Air. With a MacBook Pro, however, folks will reasonably expect to do heavier chores like photo and video editing.