Page numbers in brackets are from the hardcover, so you can check anything here against the book. How this recap was built.
Floor 10: Don't come in last
Faction Wars is over. Almost fifteen thousand crawlers took a deal and left (p. 35). Just over 5,500 kept going (p. 27), and the tenth floor tells them exactly what it wants in its name: Don't Come in Last (p. 34).
The floor is a racing tournament: seven heats on tracks the AI designed, with crawlers split into teams of up to four (p. 35) and a vehicle or mount for each team (p. 31). After every heat comes an upgrade (p. 36). Come in last and you don't move on.
The Pineapple Cabaret
Readers of the bonus stories in the print editions have been wondering about the Pineapple Cabaret for a while. Book 8 explains it: a hidden refuge outside the dungeon's playing field, built by two former crawlers, one of them a past author of the Cookbook (pp. 258-259). A place the show cannot reach is exactly the kind of thing Carl knows what to do with, and it becomes a way off the playing field for about two hundred people he could not save any other way (p. 438).
The races get worse
The tracks escalate, and the last two heats shrink the racers down and send them through a seven-floor apartment building (p. 429). Meanwhile Scolopendra, the dungeon boss the series has been warning about since the early books, starts her nine-tier attack: nine attacks, one after another (p. 661).
The field collapses. Late in the floor, most of the last thousand crawlers leave through the Outreach Guild and take a deal (p. 505), and the races kill many of the rest (p. 574). Only 23 crawlers enter the eleventh floor (p. 574), and Carl and Donut are two of them.
Floor 11: the parade
The eleventh floor opens with the parade the book is named for. The remaining crawlers are split into five float groups, and each builds its floats out of whatever is in its garages, around a theme the AI hands it (pp. 579-580).
While they march, the AI finally tells its story: what the Primals were, and why it intends to take vengeance on the Syndicate races that tried to control it, and AIs like it across the galaxy. A lot of the series' biggest questions get an answer here, and it reframes what the crawl has been about.
The arena
At the end of the route waits an arena and a floor boss (p. 579). Carl walks in with a plan made almost entirely of backup plans.
First, Emberus. Carl has been stuck with that god's quest for a long time. His tool is a pig. Penelope is beloved of Taranis, the thunder god and Emberus's own brother, and anyone who hurts her is marked for death by him (p. 141). In the arena, Emberus's heat leaves her a step from death (p. 637). Taranis kills his brother, and the quest is over.
Second, Scolopendra. Carl brings her into the arena on purpose. If she dies, the rest of her attacks trigger at once (p. 622), so killing her is off the table. His plan is to turn her into a level 1 pet and keep her locked in a pet carrier in his inventory (p. 653). The biscuit does not do what he planned. Scolopendra does not become a pet. She becomes a level 1 crawler with a mind of her own (p. 653), and a member of their party.
Where it leaves things
Nineteen crawlers are left at the end (p. 649). They go down to the twelfth floor, where the Ascendency battles are waiting (p. 600).
Book 9, The Beautiful Place, has no release date yet. The Book 9 page has everything confirmed so far.
How this recap was built
This is the short version, not a chapter-by-chapter walk-through. We started from the community wiki's chapter-cited floor pages, Wikipedia and four published reviews (listed below), and kept only events at least two of them agree on. Then we checked each one against the book itself, searching the text of the hardcover (ISBN 9798217190065) through Google Books. Every page number above is where we found it.
One detail we could not find in the searchable text: the moment Taranis kills Emberus. The book shows the setup (pp. 141 and 637), and Wikipedia and the community wiki both describe the outcome, so it stays, but it is the one claim here without a page number. Spotted something wrong? Tell us, and it gets fixed in public.