By largest, the organization doesn’t mean longest chapters, it’s literally referring to the size of the print issue. The large-scale books are exactly one meter tall and 70 cm wide, which makes them six to seven times the size of a traditional Japanese manga (Tankōbon). Furthermore, the large-scale manga weighs roughly 13.7 kilograms. This manga, of course, was part of a limited-edition release, 100 copies per chapter — the first two chapters sold out in minutes.
You can apply to purchase a copy of the large-scale Attack on Titan manga on Kodansha’s website for ¥165,000 JPY (approximately $1,540 USD).
In case you missed it, check out Attack on Titan Museum’s massive opening.