IGN interviewed the Biomutant devs:

Biomutant Developers Answer the 6 Biggest Questions

Think of a post-apocalyptic Kung Fu Panda action RPG.
By Brandin Tyrrel On the outside, BioMutant is a game about Kung Fu woodland critters in a post-apocalyptic fantasy land full of monsters, mythology, and mechs. So... yeah, it's totally understandable to still have a few questions about what's quickly becoming one of the most intriguing and anticipated games of 2018.

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How big is the open world? What will we do in it?

The world is 16 square kilometers, or approx. 6 square miles, plus some underworld areas, and you’re playing in a world that’s dying.

At the beginning of the game there’s an equilibrium; The Tree of Life that stands tall at the center of everything is struggling to survive, its five behemoth roots stretching out in all directions across the world are being gnawed on by huge creatures working their way in towards the Tree. Players have the choice to seek out these creatures at any time, trying to defeat them or entering into pacts with them – its entirely up to the player. If the creatures are defeated, it increases the likelihood the world will survive at the end of everything.

But perhaps you don’t confront the creatures at all, but instead search for Nono – small spirit potatoes that can cure the roots and help the Tree fight back. But choosing different paths will dramatically alter the experience and the end game. The world will change with your actions; the team’s goal is to create an interesting and interactive experience. As an open world RPG, exploration, discovery and interesting characters are all big parts of the game.

Much of the focus is on the characters in the world and their destiny as its in the player‘s hands. A key goal for the main character is finding out who they are and where they came from. So there’s a part of the story that is reflective and will give glimpses of the world that once where. The meat-eater you confront at the start of the game plays a part in this, as does the Narrator.

BioMutant is much more about the fate of the world as the events caused by the player’s choices are happening, and the characters that live in this world and their destiny, than retelling the history of the world that once was.

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Thanks Farflame!