When looking for a Savannah kitten or cat, you may come across the Filial (F) Number. As Savannahs are produced by crossbreeding Servals and domestic cats, each generation of Savannahs is marked with a filial number:
African Serval x Domestic cat = F1 Savannah
The percentage of wild Serval blood will vary depending on what percentage of wild blood the queen used had. For example if a domestic queen was used, the offspring will be 50% Serval but if an F1 Savannah queen with 50% wild blood was used, the offspring would be 75% Serval. And more common than a 75% F1 is a 62.5% F1 which is the product of an "A" F2 (25% female) bred back to a Serval. F1 Savannahs are very difficult to produce because of the difference in gestation periods, sex chromosomes and with male Savannahs being typically sterile until the F5 generation.
F1 x F1 Savannah = F2 Savannah
The F2 generation has a Serval grandparent and is the offspring of the F1 generation female. Their percentage of wild blood ranges from 25% to 37.5% Serval.
F2 x F2 Savannah = F3 Savannah
The F3 generation has a Serval great grandparent and is 12.5% Serval.
A Savannah to Savannah cross may also be referred to by breeders as SVxSV in addition to the filial number. Savannah generation filial numbers also have a letter designator that refers to the generation of SV to SV breeding. The letters are A, B, C and SBT.
A = One parent is a Savannah and the other is an out cross. A x (any SV) = B
B = Both parents are Savannahs and one of them is an A. B x (B,C,SBT) = C
C = both parents are B or better Savannahs and one of them is a B. C x (C, SBT) = SBT, SBT x SBT = SBT.
F1 generations Savannahs are always A since the father is a Serval. F2 generations can be A or B and F3 generations can be A, B or C. F4 Generation is the first generation that can be a championship breed SBT (Stud Book Tradition).
An SBT is also bred down from the Serval but it is at least 4 generations removed. While many F1-F5 Savannahs are diluted with domestic blood, the SBT Savannah is a "pure" Savannah that is guaranteed to only have Savannahs as parents for at least 3 generations.
Much of the information above has been sourced from Wikipedia.