You HAVE a Prius. Get a 9' long piece of something and TRY it. Or simply extend a tape measure to 9 feet. A slight bend should not be a problem.
I measured 128.5" from right corner of front window/dash to the left back corner rear window, straight shot resting on the center/left rear seat backs of my 2023 Prius Prime XSE.
I want to know what you catch when you go fishing with that. Sounds like it could help entire families.
The OP pointed out he gets a better feel with a one piece rod, vs sectional. Landing 45Lb Tuna, some of the bait we use would probably give more feel than what you would catch - fresh water fishing - as I never had any doubt when I hooked up .
Somewhere around 10-ft for Gen 2 and 3. A post wayback a guy almost gets a 10-ft kayak in there, hatch popped a little, tied shut. From that old post I purchased a 10-ft fishing kayak, but I put it in my minivan. Same idea though you need to be able to put front seat back, and second row seat down oor out (in the case of minivan). I'd get a Sienna hybrid if I thought I could do this (but 2nd seats row are permanent).
This was probably me. I fit a 10 foot kayak in my 2005 prius and the 2016 actually had a tad more room for the same kayak. Trunk closed and I didn't have to tie it shut. Bought a gen 5 and since have sold all the kayaks so didn't try.