https://wccftech.com/ghostwire-tokyo-lasts-15-hours-for-the-main-story-30-40-including-side-content/

During our Ghostwire: Tokyo interview with Tango Gameworks, we asked the developers to classify the game and share an estimate of its longevity. Game Director Kenji Kimura said the studio believes Ghostwire: Tokyo to be an action/adventure title featuring a sandbox map rather than an open world. Even so, they made sure there's lots of room to explore the city (vertically, too) and they imbued the game with quite a lot of content so that it should take around fifteen hours for the main story and between thirty and forty including the side missions.

When we were thinking about the genre of this game if this was an open world game was a question that we wanted to kind of address first in this response. Depending on your view of what an open world game things might change, but for us, we think this is an action-adventure game with a sandbox style map, with a mystery that you want to solve by exploring through the city. In that light, Ghostwire: Tokyo probably wouldn't fall into the open world genre, but that's our thinking.