@bradtem Fully purchased FSD always transfers with the car to its next owner. Always.
[ Side note: I'm not sure if monthly FSD transfers if you transfer ownership of the car mid-month. Hopefully it does, but honestly transfer of monthly FSD doesn't seem like a big deal either way, and I don't think anybody here is asking about that anyways, I'm just mentioning it for completeness. The rest of this post refers only to fully purchased FSD. ]
There is some confusion because Tesla will add or remove FSD from a car in their ownership as they see fit. Whether they own the car because it's still new (never sold to any customer yet), or because it was sold
back to them (traded in) is immaterial. They own the car and they can do what they like with it. Nothing wrong with that.
Tesla WILL NOT remove fully purchased FSD from a car not in their ownership. Yes technically they could flip their FSD config switch at any time, but they won't. If somehow they do by mistake, I'm sure they'll make it right once you notify them and show the record of FSD purchase from Tesla. This holds true no matter if the car transfers ownership - purchased FSD is transferable, to my knowledge Tesla has never sold non-transferable FSD. (Yes they have listed/sold other features as non-transferable at times, e.g. free unlimited supercharging was non-transferable on later Model S, but I've not come across non-transferable FSD.)
There is some *additional* confusion because when Tesla has removed FSD from a car in their ownership, it's possible - very rare but has happened - for FSD removal in their central system to not propagate to the car until AFTER Tesla sells the car. The next owner might then see FSD enabled, and then suddenly it's disabled/gone, and that owner
wrongly assumes they got swindled. That is not the case! In those cases Tesla never said the car came with FSD, and the next owner never verified that it was supposed to come with FSD, they just made a poor assumption based on seeing the car's currently enabled software features.
Now to be fair, given how Tesla changes software config options on cars in their ownership, it's also clearly wrong of them to sell a car before pushing the latest config to it. That should be a mandatory step in their process of selling any car (new or used), but apparently it isn't, or at least it wasn't when the scenario above made some headlines.
For extra extra confusion, that "next owner" might be an auction house, followed by a dealer, followed by an actual consumer all in very rapid order. The auction house probably doesn't know or care about FSD. Then the dealer assumes that because the car shows FSD enabled, that it's actually
supposed to, even though neither they nor the auction house have
any record from Tesla stating the car is supposed to come with FSD. (Because it's *not* supposed to have FSD anymore!) Finally the dealer advertises it with FSD, it quickly gets snapped up by a consumer, and then the consumer is upset when FSD goes away. In this case the dealer would be at fault for presenting a car as having fully purchased FSD when they had no record or promise of that from Tesla (not via the auction house and not directly either). Or if the dealer never promised that, rather the consumer just noticed it in the software menus and made an assumptions, then the consumer would be at fault.
Like with any major transaction, get the important parts in writing. If you think you're buying FSD, make sure it's in writing from the seller, so you have recourse if it turns out they don't deliver properly. Doesn't matter if the seller is an individual, a dealer, or Tesla themselves. If the seller won't promise that the car has fully purchased FSD, then assume the car doesn't truly have it and it might go away at any time when Tesla pushes a software/config update.
[ Just to be clear, I'm no fan of Tesla's "FSD," I think it looks like very poor value when purchased new from Tesla. But the FUD of Tesla removing FSD upon ownership transfer is just wrong from everything I've seen and read. Tesla only does that on cars they own, which is perfectly reasonable and within their rights. ]