One recent report said that Pluto had regained its status as the largest Kuiper Belt Object. In fact, it had never lost it, because its rival Eris isn't a Kuiper Belt Object. It's actually much farther away than the Kuiper Belt in what's called the scattered disk.
But Pluto is back to being acknowledged as the largest [known] dwarf planet, slightly larger than Eris. It hadn't been possible until now to say exactly what Pluto's diameter was because we didn't know how thick its atmosphere was.
Eris is nonetheless about 25% more massive than Pluto.
Here is what I wrote about
Pluto and Eris three years ago. No updates available about Eris, but I have some revisions to do about Pluto!