I suspect that books will be written about what his happening ~today at OpenAI, and I wouldn't be surprised if there are authors working on such books full-time now or in the near future.
Books "about OpenAI" will have to substantively (2 or more chapters, or equivalent length spread across the book) deal with the lab or the people leading it. This means a book about the race for AGI in general, for example, that covers OpenAI or Sam Altman for the requisite length will count.
"Top-selling" will be determined by total number of weeks spent on the NYT best-seller list.
This market resolves on January 1, 2030.
@Soli Very good point. I think that would be odd because "Other" reads to me as "another author." I just created a new answer that is "no book will reach the bestseller list" which will resolve yes if this happens. Hopefully that's a fair way to handle this. If anyone feels like this changes their previous bets, feel free to message me and I can compensate you.