A, B, C, or SBT?

Savannahs are produced by crossbreeding Servals and domestic cats.  Each generation of Savannahs is marked with a filial number. Cats produced directly from a Serval/domestic Cat cross are the F1 generation, and they are 50% serval.
F1 Savannahs can be as high as 75% Serval. 75% F1's are normally the offspring of a 50% F1 (true F1) female bred back to a Serval. There have been cases of 87.5% F1 (technically BC2)Savannah cats but fertility is questionable at those percent Serval levels. More common than a 75% F1 is a 62.5% F1 which is the product of an "F2A" (25% Serval, female) bred back to a Serval. The F2 generation, which has a Serval grandparent and is the offspring of the F1 generation female, ranges from 25% to 37.5% Serval. The F3 generation has a Serval great grandparent, and is 12.5% Serval.

A Savannah/Savannah cross, which is what we produce here at Northeast Savannah, may also be referred to as SVxSV (SV is the TICA code for the Savannah breed), 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 designation of A means that one parent is a Savannah and the other is an outcross. B is used for both parents are Savannahs with one of them being an "A". "C" is both parents are Savannahs and one of them is a "B". Therefore A x (any SV) = B; B x (B,C,SBT) = C; C x (C, SBT) = SBT, SBT x SBT = SBT. F1 generations Savannahs are always A since the father is a non-domestic outcross (the Serval father). F2 generation can be A or B. F3 generation can be A, B or C. F4 Generation is the first generation that can be a SBT. SBT stands for "stud book tradition" and is considered a "purebred" cat. Males are sterile prior to the 5th generation, although it is recommended that they are neutered.

The International Cat Association (TICA) considers the "SBT" (studbook tradition) Savannah, eligible for competition in the show ring and a fully accepted domestic cat.

Here in Massachusetts, it is illegal to own a cat prior to the fourth generation. 

Please review the hybrid laws for your state.  The law can be found at http://www.hybridlaw.com/