"There is nothing short term about my intentions here," he said.
Carl Icahn now owns about 0.5% of Apple.
In a letter to Tim Cook, Icahn suggested that three years after the buyback, with the benefit of earnings growth, Apple's shares could hit $1,250.
Apple has already launched a plan to return $100 billion to shareholders, including a $60 billion buyback, over the next three years. Referring to that plan in his letter, Icahn wrote that while it "may seem like a large buyback, it is simply not large enough given that Apple currently holds $147 billion of cash on its balance sheet."
Icahn in August disclosed via Twitter that he was talking to Cook. Earlier this month he also said he had dinner with Apple's boss for the buyback.