Adopt Me! is a free-to-play experience available on the Roblox platform. As long as Roblox continues to be free as a platform, Adopt Me! will also remain free.
There are purchasable premium items within Adopt Me! available with Robux, however, this is not necessary.
Most areas are accessible within the game without the need to purchase, with the exception of the VIP area which is a private space for VIP Gamepass holders to hang out in however being unable to access this does not restrict gameplay.