Ashbutt has been growing by leaps and bounds. A month after he came home, he's already twice the size of the kitten who slept most of the way home. The growth doesn't look like it's slowing down any time, soon. He has more rambunctious energy than two humans and an adult cat can deal with (and today he learned how to climb legs encased in socks. Ow.) He also purrs, near-frantically, at almost everything. Including the food bowl, where he's eating more than Kili does, and has also quickly learned to show up when she gets treats.
To date, I've heard two faint, tiny little chirps out of him, and one gigantic squall when he dashed underfoot and said foot landed on his tail. (Well, at least we know he's not mute.) But an extremely quiet cat, purrs aside.
Tonight, I realized his tail is already fluffier than Kili's fully adult tail. This bodes a long-fur fluffy future. With some trepidation, I did more internet searching, and happened upon some incredibly close matches to his own kittenish frame and coloration.
They both had the caption: "Black Smoke Maine Coon Cat"