What it says above: Tantor will be publishing audio books of all the Twenty Palaces novels (and that novella) and the first one will come out June 10th.
Audible has made the book available for pre-order, which you can do right now if you like.
As I write this, that’s the only place where it’s listed, but if you have a favorite audio vendor, I’m sure it’ll be there soon.
And the rest of the series arrives throughout the rest of the summer, one book per month. I’ll send a newsletter later this year, to announce all of them at once rather than spamming your inboxes once a month.