It's been accidentally disclosed a few times over the years. IIRC at some point someone offered to sell the recipe to Pepsi, and they refused on account of the legal mess it would put them in and perhaps a sense of honor
And the fact that "Pepsi Coke" is a marketing non-starter; they want people to buy Pepsi, and the people who won't buy Pepsi, but will buy Coke...will just buy Coke, not Pepsi Coke.
