They're available for a limited-time as an upgrade over the standard tots in a combo or alone and look to be pretty interesting.
In addition to the new menu item, Sonic is also offering a limited-time deal of a "snack-size" portion of their Jumbo Popcorn Chicken for $1.99 after 8pm.
Nutritional Info - Sonic Sweet Potato Tots (187g)
Calories - 290 (from Fat - 70)
Fat - 8g (Saturated Fat - 0g)
Sodium - 510mg
Carbs - 51g (Sugar - 18g)
Protein - 1g