WASHINGTON — The fourth Democratic presidential debate will feature the biggest stage ever, with 12 candidates together for one night only, the debate's sponsors announced Wednesday.

The Oct. 15 event at Otterbein University in Westerville, Ohio, just outside Columbus, will include every candidate who qualified, instead of splitting the massive field over two nights as Democrats did in their first two debates earlier this year, when no more than 10 candidates appeared together.

Former Vice President Joe Biden and Massachusetts Sen. Elizabeth Warren, will be centerstage, reflecting their lead in polls, while lower-performing candidates were placed towards the wings.

Biden will have progressive rivals on both sides of him — Warren to his left and Vermont Sen. Bernie Sanders, I-Vt. to his right, while Mayor Pete Buttigieg of South Bend, Indiana will be on Warren's other side.

The next rung out will feature California Sen. Kamala Harris and entrepreneur Andrew Yang, followed by New Jersey Sen. Cory Booker and former Texas Rep. Beto O'Rourke.

Filling out the rest of the stage will be Minnesota Sen. Amy Klobuchar, billionaire Tom Steyer, Hawaii Rep. Tulsi Gabbard and former Housing Secretary Julián Castro.

The only newcomer to the 2020 debates will be Steyer, who entered the race late but has already spent at least $17 million of his own money on TV and radio ads to catch up.

All 12 candidates met the Democratic National Committee's qualifications for the CNN/New York Times debate, which included registering at least two percent in four qualifying polls and receiving donations from at least 130,000 online donors.

The bar to qualify for the November debate has been raised to 3 percent in four polls, as well as 165,000 donors.

Democratic voters have expressed frustration with the size of the largest presidential primary field in history and told pollsters they're eager for the field to winnow.

Still, several candidates who failed to qualify for the October debate have said they are regardless staying in the race.

One of them, former Maryland Rep. John Delaney, saw four top aides — including his communications director and a senior adviser— depart the campaign this week.

"Love John and am rooting for him. But it was time for me to move along," John Davis, a veteran Iowa operative who was Delaney's campaign manager before transitioning to a senior adviser role, told NBC News.