Ubisoft has stated from the get-go, that Assassin's Creed Odyssey will be larger than its predecessor, Assassin's Creed Origins. While we now know that to be true, it seems to be a truth with modifications.
Recently, trophy hunter and guide writer PowerPyx unveiled the game's full map, and while it's strictly larger than Origins' map, the majority of it is water.
The game world is 130 square kilometeres, which is 62% bigger than the world in Origins' 80 square kilometers. The land mass, however, is smaller. Then again, from what we've experienced the gameplay is very dense on the island, and Origins featured large desert areas without much actual content.
You can see the full map below.