What do the letters mean?

The letter after the generation comes from TICA’s registration codes that designate how many generations of savannah parentage a cat has.
F2 ‘A’ or F3 ‘A’ = cat with one savannah and one domestic parent
F2 ‘B’ or F3 ‘B’ = cat with two savannah parents
F3 ‘C’ = cat with two generations of savannah X savannah breeding (both parents and grandparents are all savannahs)
F4 ‘C’ = same as C above (but with at least one non-savannah great-grandparent)
F4 ‘SBT’ = cat with three generations or more of savannah X savannah breeding (parents, grandparents, great-grandparents are all savannahs)

SBT stands for ‘stud book traditional’ and is TICA’s designation for cats that have no outcrosses for a minimum of 3 generations. Only SBT cats are able to participate in TICA shows and eligible for championship status. (Because cats at the F1, F2 and F3 generations have a serval ancestor within 3 generations, they cannot be SBT. F4 is the first generation that can be SBT).