George R. R. Martin has released a number of works in the “A Song of Ice and Fire” (ASOIAF) universe since his 1996 novel “A Game of Thrones”. The most recent work in the universe was “Fire & Blood”, an in-universe history book published in 2018, while the main series of ASOIAF novels is still unfinished, with five of a projected seven novels published. Martin’s age (he was born in 1948) and slow progress with the books has led to concerns among fans that the main series and “Dunk and Egg” novellas will not be finished.

This market resolves to the next book or story (eg a short story in an anthology) officially written by Martin (possibly with a collaborator or collaborators) and released within his lifetime. Books and stories must have substantial new content (eg a book consisting of an extract of “Fire & Blood” would not count), though they may overlap (eg a second volume of “Fire & Blood” would likely have some content in common with “The World of Ice and Fire”). An official release is needed, so leaks would not count. If multiple works release on the same day then the answers will resolve to PROB (though this seems unlikely).

A book in the main ASOIAF series could be “The Winds of Winter”, but any novel that is the sequel to “A Dance with Dragons” would count (such as a sequel with only half the POV characters, like “A Feast for Crows”). A new sample chapter would not count (for this answer or for any answer).

A different fiction book/story could for example be a novel about Aegon IV from his POV, or a murder mystery set in the Free Cities (both of which are ideas Martin has mentioned: https://www.westeros.org/Citadel/SSM/Entry/Interaction_Glasgow_Scotland_UK_August_4_81).

A different in-universe non-fiction book could for example be the in-universe history book “The Nine Voyages”, which could be written as a tie-in to an animated show about the Sea Snake Corpus Velaryon (https://old.reddit.com/r/asoiaf/comments/18z9e87/spoilers_extended_the_nine_voyages_dunk_egg_and/).

One ambiguous case is if Martin published a book consisting of one or two characters’ chapters from “The Winds of Winter” (eg he has said that he has written enough Arya chapters to make a novella). I think the main way I would decide whether this is “a book in the main ASOIAF series” or “a different fiction/book story” would be whether Martin considers it to be the sixth book in the series or not (but I would lean towards the latter for anything novella-length).

I think these options should cover all the possible works he could release, but please do ask for clarification if needed! Owing to the possible ambiguities I won’t bet in this market.