Amazon UK now list Antkind's release date as 14 May 2020, with 336 pages.
Amazon US have it as 6 February 2020.
Both sites list Charlie as the author, and the temporary cover image lists William Mulligam as the author.
Why? I don't know. WHY?
But here's a thing: Antkind has a second page on Amazon US, where Random House is listed as the publisher, the release date is May 12, the page count sits at 752 (which is about what I'd expected from Charlie, to be honest), and there's no reference to William Mulligam. In the US, Charlie was originally slated to be published by Grand Central, a division of Hachette. Random House are an entirely different company. Has Charlie switched publishers? Is that somehow connected to the new William Mulligam image on the old Amazon page? Or has Amazon lost its mind? Or have I lost mine?
I Googled "William Mulligam" and only pages for this book came up. So then I Googled "Mulligam" by itself, and "Mulligam Syndrome" and "Mulligam Disorder," because Charlie likes weird mental disorders and has a hankering for giving characters names with hidden meanings (Synecdoche, New York's Caden Cotard was named for Cotard delusion, and Charlie originally wrote Anomalisa for the stage under the pseudonym Francis Fregoli, after Fregoli delusion)... but I came up with nothing.
The good news is if you Google "Antkind," a whole load of publishers and bookstores show up in the results (e.g. HarperCollins here in Australia), which means Charlie's novel (OR WILLIAM'S) is so far still a thing that is actually happening. There are pre-order buttons here and there, but I wouldn't count on the release date until we see some marketing for the book.
Thanks to Livia, Jonah, Thomas, and u/staresAwkwardly on r/kaufman