They haven't announced anything, but the quote in the story is:

Delta is replacing its fleet of Boeing 747s with Boeing’s new, fuel-efficient 787 aircraft and Airbus A350s. “That fleet is going to unlock longer-haul markets,” Anderson said.

To me, it sounds like pretty specific. If he had said, "airplanes like that" then it's just conjecture. But reports miss-quote things sometimes or take things out of context.

Personally I don't think the A350 is mature enough for us to order, but that's just me.