In an interview, he said:

After writing two nonfiction books, I do miss writing fiction and feel called back to it, so that’s what I’m working on now ...

I think [my next book will be fiction], but if you had asked me after my previous book, I would have said the same. I never imagined I would go down this rabbit hole with TB.

His past two books, Everything is Tuberculosis (2025) and The Anthropocene Reviewed (2021) were nonfiction. Prior to that, he authored or coauthored seven fiction novels, most recently Turtles All the Way Down (2017) and The Fault in Our Stars (2012).

I will extend this market until John Green releases another book, although I will resolve N/A if it becomes clear that he will never release another book. If it is ambiguous whether his next book is fiction, I will use my best judgement.

General policy for my markets: In the rare event of a conflict between my resolution criteria and the agreed-upon common-sense spirit of the market, I may resolve it according to the market's spirit or N/A, probably after discussion.