@awnlee jawking
I was unable to find any publishers who admitted to using Chicago.
From Writer's Digest:
According to Formatting & Submitting Your Manuscript (and editors I've spoken to at conferences), most book publishers use The Chicago Manual of Styleβor some variation of itβas a formatting guide for their books.
From acrolinx:
Currently on its 17th edition, The Chicago Manual of Style is beloved by writers, editors, and publishers. It's the standard for book publishing in fiction and nonfiction and is often used in the arts and humanities for academic papers.
And from University of Chicago:
Intended originally as a guide for publishers of academic books and journals, it is especially popular in the humanities and social sciences. Chicago style is also used widely by students and by publishers of novels and trade books.
From reddit (with some answers):
Q: I'm a freelance editor. I have about 3 years' experience, mostly fiction. Everything I've read says the standard style (beyond their in-house guides) for traditional, American fiction publishers is Chicago Manual of Style. I even happened to check 4 semi-recent hardcover novels on my shelf today and they all use CMS ellipses and em dashes. But I just handed back my proofreading to a client and they claim that Chicago Manual of Style is not for fiction, only nonfiction. What?!
A1: I'm a production editor at a Big 5 house and "Chicago is only for nonfiction" is not a thing. We use it for everything.
A2: Have worked for several publishers of fiction. All use Chicago
A3: Officially, CMS is for "formal" nonfiction writing, but as I've seen by comments above & suspected, many many fiction publishing houses do base their in-house style guides off it.