Savannah cats tend to become larger than the average breed. But in the early days of the Savannah, references were often made as to the enormous size of this breed. That aspect was over-emphasized, possibly because the first Savannahs by definition belonged to higher generations. These tend to be larger than their counterparts of lower generations. But even the adult size of an F1 or F2 Savannah can vary, and size is not considered the most important quality in Savannahs.
Because of this historical exaggeration, many prospective Savannah-owners will even to this day inquire about the eventual size of the kitten they are about to buy. Although it will almost certainly be huge in personality, no breeder should give you any guarantee as to the eventual size. If it does turn out to be a whopper, consider this a bonus if you like. If not, you still have the cutest cat with a great personality!
If you encounter a breeder who states that his/her kitten is guaranteed to become a huge adult, ask for confirmation in writing! Through experience with certain bloodlines they may be able to make a guess. But even the biggest kitten in a litter may not carry that qualification any more as an adult. And a runt may possibly even surpass it in size.
Even the size of the respective parents is not a reliable guide as to the size of the offspring. If anything, former produce of the same pairing (if available) may give you a hint as to what to expect with regard to size. But even this would be a guess, albeit a more educated one.
Conclusion: we can never give you any guarantee as to the eventual size of our kittens.