A couple days after you read it here, Entertainment Weekly made it official:

[...] The Oscar-winning screenwriter behind such acclaimed cult-classics as Being John Malkovich, Adaptation, Eternal Sunshine of the Spotless Mind, Synecdoche, New York, and Anomalisa has landed a deal with Random House to publish his debut novel, Antkind, EW can announce exclusively. The publisher, which originally acquired the book in 2012, describes it as a “mind-bending opus.”

[...]“There are no budgetary limitations in a novel,” [Charlie] said in a statement. “There is no studio oversight. There are no focus groups. In fact, this book is in part about that; it’s about an impossible movie.”

Ben Greenberg, VP and Executive Editor at Random House, adds: “I’ve been talking to Charlie about this novel for almost eight years and watching it change and recalibrate and grow. Antkind is a hilarious, devastating, epic mindf–k. I’ve never read anything else like it.” (Source)

They also exclusively reveal the cover BCK showed you a couple days earlier.