An Infinite Saiyan has infinite power. The power is too much to have all at one time, which is why Old Kai created methods of restricting the Infinite Saiyan form. The transformation becomes your base form. Gohan was the first to reach the state. He was followed by, in order, Vegeta, Future Trunks, Broly, Goten, Pan, Bulla, Trunks, and all the other saiyans on earth. Goku had to work in 1,000,000,000 times earth's gravity before he transformed. Infinite Saiyan comes after SS10, but you don't have to be Super Saiyan Ten to achieve the form.