Yeah, you are required to pay a much more expensive subscription in order to access Netflix Originals at 4K resolution.You have to pay extra for 4K Netflix anyway so you're not going to accidentally get it! Most sites allow you to choose the quality and few have much actual 4K content (I don't use the BBC so can't comment on that).
We have a 4K TV and even though most content isn't natively so, it manages decently enough.
Meanwhile Amazon Prime, on the other hand, offers 4K Ultra HD at no extra cost. That's right, if you have a Prime sub, you got access to titles like The Boys, Carnival Row and Suspiria at UHD quality. Surprising isn't it?