As far as I know this guy is correct.
Originally Posted by
mstateglfr
.... if you get STI shifters where the cables exit the side of the shifter in the middle of the bike(vs hidden under tape), you should be good. This means older ultegra or 105 will work too. Keep it to 9 speed and there will not be a problem at all.
First-gen 10-speed Tiagra (4600) is included.