steve:
Maybe..... The City One is carbon fiber, and does not come with any rack mounts. The owner's manual is full of warnings about how not to abuse the CF. The only fittings are for the fenders, which mount with 3 mm screws. I've spoken to a shop that does CF repairs & they say it may be possible but they want to see the rack & know what kinds of loads I intend to carry. I haven't followed thru with a visit to them.
Without frame mods, it may be possible to use the rear fender mounting points if the 3 mm screws will take the load. By comparison, standard touring bike rack mounts are 5 or 6 mm, and are meant for loads of as much as 50 lbs. My opinion is that if the rack + load did not exceed 10 lbs, the little screws and their related frame fittings would be OK. One would have to slip a narrow strap, perhaps no thicker than 1/16", between the fender & its upper mounting point, and use the fender mounts on the lower stays for the vertical rack struts. An alternative would be a seatpost collar the has rack mounts, but the seatpost is also CF.
I know how useful a rack can be, and have had racks on my bikes for over 30 years. Depending on what you need to carry, and how accessible it needs to be while riding, the world is full of all kinds of bikepacking bags that intended for rackless bikes. I have a fat little saddlebag that holds my tools, tube & lock, and a 7 liter handlebar bag for larger things. A computer, books, packages, groceries, etc. could be a problem.
Doug