The worldbuilding premise here is that this world previously had cities run by AI gods (yes, exactly that problematic of a power dynamic) who have mostly become corrupted and destroyed. The Harbor builds giant ENGINE robots from corrupted god corpses as a protection mechanism against frenzied robotic fragments of those same gods. Sunai was in contact with Iterate Fractal (the AI of Khuon Mo) when it died, and became immortal and unaging. He's tried to run away and escape, but when he hears that the Harbor has seemingly impossibly built an ENGINE from Iterate Fractal he's eventually sucked back into trying to understand why and maybe kill and/or save what he can of the scraps of Iterate Fractal.
(Yes, all of the AIs have amazing names like Reconcile Elegy, Perish Aflame, and Fun-Sized Exultation in Perpetuity.)
This book asked a lot of me as a reader. It's very dissociative, literally and figuratively. There's buried betrayals, backstabbing, and ongoing playing of both sides. Character motivations also change over time, and so there's never a simple answer to why and what they want. There's even some antimemetic properties in play where people have done things they don't remember. There's trauma big and small and divine. There's a surprising amount of sudden second person perspective shifts, flashbacks, and mental interjections of things both Sunai and the reader don't understand. There are excellent authorial reasons for all of these choices that pay off in the end but ... it's also A LOT.
"I guess, it's just, is there something I should know about archivists?" Dzira uses the Imperial Standard word for "archivist"--the one with connotations of libraries and record-keeping. The word in Mohani is a synonym for "vital organs."
Much akin to Ninefox Gambit and the Machineries of Empire series, The Archive Undying drops you into a world and doesn't bother to explain what basic words mean. Words like "relic" and "ENGINE" and "frags" mostly got explained to me in the end, but I am still not sure I could explain to you what an "archive" is more generally. Personally, this ambiguity was catnip for me and I dig a slow burn lore reveal.
In a similar worldbuilding sense, I also feel like this book drops you in halfway and doesn't give you a helping hand. There's a lot of backstory that gets handwaved at, such as a Cradle that was abandoned, previous wars where the Harbor got started, and what the heck even is the Immaculate Empire. It's all delicious and I want to know it all but it felt akin to reading Witch King recently where you almost wish there was a previous or follow-up book to just to dig into everything happening on the sidelines. However, all of this world context is just marginalia to a story that focuses on one specific dead god and its city, two "individuals" in emotional orbit around it and each other, and the fluctuating love/hate relationships connecting all of them together.
All of this makes a lot of the book very crunchy and messy. I had to be very engaged while reading it, but I felt an ongoing intrigued frustration with the uncertainty and unknown that kept me interested. It all worked for me, but I would give this a conditional recommendation.