Source: https://store.steampowered.com/news/app/1301290/view/541102606924120125

“Hi! In the coming months, I’ll be working hard to properly update the game (total conversion) and make significant changes to make it even more fun and destructive than before. Therefore, I’ll be updating to a paid version. Those who have already downloaded the game will be able to upgrade to the new version. Thank you for your understanding.”