The cool cats at iFixit have just published their teardown of the 13-inch 2018 Touch Bar MacBook Pro, the results indicating larger battery and speaker components, which appear to have come without an increase in overall weight.
The notebook has been upgraded from a five-cell, 49.2 watt-hour battery to a 58 watt-hour six-cell part. The battery is indeed slightly heavier, up to 232.7 grams (8.2 ounces) versus 196.7 (6.9 ounces). Updated speakers are both “longer and narrower,” to the point that they bump up against the logic board.
Per the report, Apple appears to have pared down the weight of the top case as a means of compensation for the weight increase.