Now this active gardening group of forums probably isn't going to support the full spectrum of what a giant tomato can be. That said: Many of our growers do have access to a set of scales. And wouldn't mind having some bragging rights. Your giant tomato needs a photo of it upon a scale. Weight shall be the sole determiner of giantism. It should grow from a single stem (it may have a compound or mega blossom scar), but must be a single fruit. This year I am due to grow Tennessee Britches, Cherokee Chocolate, and Thessaloniki Ox-hearts. All have grown one Kilo fruit on past years. I don't know if there is a giant in my seed vials or not. Time will tell.
Good luck with your tomatoes and do let us see the giant you will, potentially be growing, when it's ripe for picking.
Yep ! Thats the one. I forgot who suggested it first. Give you a brownie button! I think it will be fun.