Credit: Manuel Balce Ceneta/AP Photo

With all the talk of Hillary Clinton's political ambitions in the air, Vice President Joe Biden isn't being outdone: He's now speaking at Sen. Tom Harkin's annual steak fry in Iowa next month, ABC News has learned.

San Antonio Mayor Julian Castro is already the marquee speaker for the Sept. 15 event, but Biden will deliver a speech after Castro. It was Biden's idea to attend, people with knowledge of the event said, and he raised it with Harkin.

An aide to Biden told ABC News Sunday night that the invitation was "a long-standing commitment," after Biden was invited, but unable to attend last year.

The appearance by Biden raises the intrigue surrounding his political future. He has not ruled out making his own run for the White House in 2016 and plans to spend the next two years delivering highly visible political speeches to help lay the groundwork if he decides to run.

"He loves this," a longtime Biden associate said.

The Harkin Steak Fry is a political tradition, where a young Sen. Barack Obama made his Iowa debut in 2006. Castro is still delivering the keynote speech next month, but Biden's appearance will draw even more attention.