The Ballydoyle handler has saddled 10 previous winners of the seven-furlong Group Two, with Giant's Causeway (1999), Hawk Wing (2001), Gleneagles (2014) and this year's dual 2000 Guineas hero Churchill (2016) among those on the roll of honour.
This year's representatives all seemingly need to improve to score at Group Two level, with none of the trio having won their most recent starts.
Rostropovich opened his account on his second appearance at Gowran Park, but was a disappointing odds-on favourite at Naas last time.
Berkeley Square won nicely at Tipperary before finishing well-held in a Group Three, while Coat Of Arms has been placed in maidens the last twice.
"We run a few in the Futurity. Rostropovich was disappointing the last day but we think he might improve," said O'Brien.
Ger Lyons saddles a major contender in Camelback, who steps up in class following successive wins at Leopardstown and Naas.
Lyons said: "He'll have to behave himself. He's a nice horse, but mentally he's not there yet.
"He's short of that class, but he's there and it will be another step in his education."
The Jim Bolger-trained Theobald sets the standard after filling the runner-up spot in the Anglesey and Tyros Stakes on his last two appearances.
Joe Murphy's twice-raced maiden Swiss Cottage completes the line-up.